Thi thử VSTEP online đề Văn Lang #1 test 4 reading part 1

READING TEST 4

PASSAGE 1 – Questions 1-10

Just as optical fibers have transformed communication, they are also revolutionizing medicine. These ultra-thin, flexible fibers have opened a window into the living tissues of the body. By inserting optical fibers through natural openings or small incisions and threading them along the body's established pathways, physicians can also look into the lungs, intestines, heart, and other areas that were formerly inaccessible to them.

The basic fiber-optics system is called a fiberscope, which consists of two bundles of fibers. One, the illuminating bundle, carries light into the tissues. It is coupled to a high-intensity light source. Light enters the core of the high-purity silicon glass and travels along the fibers. A lens at the end of the bundle collects the light and focuses it into the other bundle, the image bundle. Each fiber in the bundle transmits only a tiny fraction of the total image. The reconstruction image can be viewed through an eyepiece or displayed on a television screen. During the last five years, improved method of fabricating optical fibers have led to a reduction in fiberscope diameter and an increase in the number of fibers, which in turn has increased resolution.

Optical fibers can also be used to deliver laser light. By use of laser beams, physicians can perform surgery inside the body, sometimes eliminating the need for invasive procedures in which healthy tissue must be cut through to reach the site of disease. Many of these procedures do not require anesthesia and can be performed in a physician's office. These technique have reduced the risk and the cost of medical care.

READING TEST 4

PASSAGE 1 – Questions 1-10

Just as optical fibers have transformed communication, they are also revolutionizing medicine. These ultra-thin, flexible fibers have opened a window into the living tissues of the body. By inserting optical fibers through natural openings or small incisions and threading them along the body's established pathways, physicians can also look into the lungs, intestines, heart, and other areas that were formerly inaccessible to them.

The basic fiber-optics system is called a fiberscope, which consists of two bundles of fibers. One, the illuminating bundle, carries light into the tissues. It is coupled to a high-intensity light source. Light enters the core of the high-purity silicon glass and travels along the fibers. A lens at the end of the bundle collects the light and focuses it into the other bundle, the image bundle. Each fiber in the bundle transmits only a tiny fraction of the total image. The reconstruction image can be viewed through an eyepiece or displayed on a television screen. During the last five years, improved method of fabricating optical fibers have led to a reduction in fiberscope diameter and an increase in the number of fibers, which in turn has increased resolution.

Optical fibers can also be used to deliver laser light. By use of laser beams, physicians can perform surgery inside the body, sometimes eliminating the need for invasive procedures in which healthy tissue must be cut through to reach the site of disease. Many of these procedures do not require anesthesia and can be performed in a physician's office. These technique have reduced the risk and the cost of medical care.

READING TEST 4

PASSAGE 1 – Questions 1-10

Just as optical fibers have transformed communication, they are also revolutionizing medicine. These ultra-thin, flexible fibers have opened a window into the living tissues of the body. By inserting optical fibers through natural openings or small incisions and threading them along the body's established pathways, physicians can also look into the lungs, intestines, heart, and other areas that were formerly inaccessible to them.

The basic fiber-optics system is called a fiberscope, which consists of two bundles of fibers. One, the illuminating bundle, carries light into the tissues. It is coupled to a high-intensity light source. Light enters the core of the high-purity silicon glass and travels along the fibers. A lens at the end of the bundle collects the light and focuses it into the other bundle, the image bundle. Each fiber in the bundle transmits only a tiny fraction of the total image. The reconstruction image can be viewed through an eyepiece or displayed on a television screen. During the last five years, improved method of fabricating optical fibers have led to a reduction in fiberscope diameter and an increase in the number of fibers, which in turn has increased resolution.

Optical fibers can also be used to deliver laser light. By use of laser beams, physicians can perform surgery inside the body, sometimes eliminating the need for invasive procedures in which healthy tissue must be cut through to reach the site of disease. Many of these procedures do not require anesthesia and can be performed in a physician's office. These technique have reduced the risk and the cost of medical care.

READING TEST 4

PASSAGE 1 – Questions 1-10

Just as optical fibers have transformed communication, they are also revolutionizing medicine. These ultra-thin, flexible fibers have opened a window into the living tissues of the body. By inserting optical fibers through natural openings or small incisions and threading them along the body's established pathways, physicians can also look into the lungs, intestines, heart, and other areas that were formerly inaccessible to them.

The basic fiber-optics system is called a fiberscope, which consists of two bundles of fibers. One, the illuminating bundle, carries light into the tissues. It is coupled to a high-intensity light source. Light enters the core of the high-purity silicon glass and travels along the fibers. A lens at the end of the bundle collects the light and focuses it into the other bundle, the image bundle. Each fiber in the bundle transmits only a tiny fraction of the total image. The reconstruction image can be viewed through an eyepiece or displayed on a television screen. During the last five years, improved method of fabricating optical fibers have led to a reduction in fiberscope diameter and an increase in the number of fibers, which in turn has increased resolution.

Optical fibers can also be used to deliver laser light. By use of laser beams, physicians can perform surgery inside the body, sometimes eliminating the need for invasive procedures in which healthy tissue must be cut through to reach the site of disease. Many of these procedures do not require anesthesia and can be performed in a physician's office. These technique have reduced the risk and the cost of medical care.

READING TEST 4

PASSAGE 1 – Questions 1-10

Just as optical fibers have transformed communication, they are also revolutionizing medicine. These ultra-thin, flexible fibers have opened a window into the living tissues of the body. By inserting optical fibers through natural openings or small incisions and threading them along the body's established pathways, physicians can also look into the lungs, intestines, heart, and other areas that were formerly inaccessible to them.

The basic fiber-optics system is called a fiberscope, which consists of two bundles of fibers. One, the illuminating bundle, carries light into the tissues. It is coupled to a high-intensity light source. Light enters the core of the high-purity silicon glass and travels along the fibers. A lens at the end of the bundle collects the light and focuses it into the other bundle, the image bundle. Each fiber in the bundle transmits only a tiny fraction of the total image. The reconstruction image can be viewed through an eyepiece or displayed on a television screen. During the last five years, improved method of fabricating optical fibers have led to a reduction in fiberscope diameter and an increase in the number of fibers, which in turn has increased resolution.

Optical fibers can also be used to deliver laser light. By use of laser beams, physicians can perform surgery inside the body, sometimes eliminating the need for invasive procedures in which healthy tissue must be cut through to reach the site of disease. Many of these procedures do not require anesthesia and can be performed in a physician's office. These technique have reduced the risk and the cost of medical care.

READING TEST 4

PASSAGE 1 – Questions 1-10

Just as optical fibers have transformed communication, they are also revolutionizing medicine. These ultra-thin, flexible fibers have opened a window into the living tissues of the body. By inserting optical fibers through natural openings or small incisions and threading them along the body's established pathways, physicians can also look into the lungs, intestines, heart, and other areas that were formerly inaccessible to them.

The basic fiber-optics system is called a fiberscope, which consists of two bundles of fibers. One, the illuminating bundle, carries light into the tissues. It is coupled to a high-intensity light source. Light enters the core of the high-purity silicon glass and travels along the fibers. A lens at the end of the bundle collects the light and focuses it into the other bundle, the image bundle. Each fiber in the bundle transmits only a tiny fraction of the total image. The reconstruction image can be viewed through an eyepiece or displayed on a television screen. During the last five years, improved method of fabricating optical fibers have led to a reduction in fiberscope diameter and an increase in the number of fibers, which in turn has increased resolution.

Optical fibers can also be used to deliver laser light. By use of laser beams, physicians can perform surgery inside the body, sometimes eliminating the need for invasive procedures in which healthy tissue must be cut through to reach the site of disease. Many of these procedures do not require anesthesia and can be performed in a physician's office. These technique have reduced the risk and the cost of medical care.

READING TEST 4

PASSAGE 1 – Questions 1-10

Just as optical fibers have transformed communication, they are also revolutionizing medicine. These ultra-thin, flexible fibers have opened a window into the living tissues of the body. By inserting optical fibers through natural openings or small incisions and threading them along the body's established pathways, physicians can also look into the lungs, intestines, heart, and other areas that were formerly inaccessible to them.

The basic fiber-optics system is called a fiberscope, which consists of two bundles of fibers. One, the illuminating bundle, carries light into the tissues. It is coupled to a high-intensity light source. Light enters the core of the high-purity silicon glass and travels along the fibers. A lens at the end of the bundle collects the light and focuses it into the other bundle, the image bundle. Each fiber in the bundle transmits only a tiny fraction of the total image. The reconstruction image can be viewed through an eyepiece or displayed on a television screen. During the last five years, improved method of fabricating optical fibers have led to a reduction in fiberscope diameter and an increase in the number of fibers, which in turn has increased resolution.

Optical fibers can also be used to deliver laser light. By use of laser beams, physicians can perform surgery inside the body, sometimes eliminating the need for invasive procedures in which healthy tissue must be cut through to reach the site of disease. Many of these procedures do not require anesthesia and can be performed in a physician's office. These technique have reduced the risk and the cost of medical care.

READING TEST 4

PASSAGE 1 – Questions 1-10

Just as optical fibers have transformed communication, they are also revolutionizing medicine. These ultra-thin, flexible fibers have opened a window into the living tissues of the body. By inserting optical fibers through natural openings or small incisions and threading them along the body's established pathways, physicians can also look into the lungs, intestines, heart, and other areas that were formerly inaccessible to them.

The basic fiber-optics system is called a fiberscope, which consists of two bundles of fibers. One, the illuminating bundle, carries light into the tissues. It is coupled to a high-intensity light source. Light enters the core of the high-purity silicon glass and travels along the fibers. A lens at the end of the bundle collects the light and focuses it into the other bundle, the image bundle. Each fiber in the bundle transmits only a tiny fraction of the total image. The reconstruction image can be viewed through an eyepiece or displayed on a television screen. During the last five years, improved method of fabricating optical fibers have led to a reduction in fiberscope diameter and an increase in the number of fibers, which in turn has increased resolution.

Optical fibers can also be used to deliver laser light. By use of laser beams, physicians can perform surgery inside the body, sometimes eliminating the need for invasive procedures in which healthy tissue must be cut through to reach the site of disease. Many of these procedures do not require anesthesia and can be performed in a physician's office. These technique have reduced the risk and the cost of medical care.

READING TEST 4

PASSAGE 1 – Questions 1-10

Just as optical fibers have transformed communication, they are also revolutionizing medicine. These ultra-thin, flexible fibers have opened a window into the living tissues of the body. By inserting optical fibers through natural openings or small incisions and threading them along the body's established pathways, physicians can also look into the lungs, intestines, heart, and other areas that were formerly inaccessible to them.

The basic fiber-optics system is called a fiberscope, which consists of two bundles of fibers. One, the illuminating bundle, carries light into the tissues. It is coupled to a high-intensity light source. Light enters the core of the high-purity silicon glass and travels along the fibers. A lens at the end of the bundle collects the light and focuses it into the other bundle, the image bundle. Each fiber in the bundle transmits only a tiny fraction of the total image. The reconstruction image can be viewed through an eyepiece or displayed on a television screen. During the last five years, improved method of fabricating optical fibers have led to a reduction in fiberscope diameter and an increase in the number of fibers, which in turn has increased resolution.

Optical fibers can also be used to deliver laser light. By use of laser beams, physicians can perform surgery inside the body, sometimes eliminating the need for invasive procedures in which healthy tissue must be cut through to reach the site of disease. Many of these procedures do not require anesthesia and can be performed in a physician's office. These technique have reduced the risk and the cost of medical care.

READING TEST 4

PASSAGE 1 – Questions 1-10

Just as optical fibers have transformed communication, they are also revolutionizing medicine. These ultra-thin, flexible fibers have opened a window into the living tissues of the body. By inserting optical fibers through natural openings or small incisions and threading them along the body's established pathways, physicians can also look into the lungs, intestines, heart, and other areas that were formerly inaccessible to them.

The basic fiber-optics system is called a fiberscope, which consists of two bundles of fibers. One, the illuminating bundle, carries light into the tissues. It is coupled to a high-intensity light source. Light enters the core of the high-purity silicon glass and travels along the fibers. A lens at the end of the bundle collects the light and focuses it into the other bundle, the image bundle. Each fiber in the bundle transmits only a tiny fraction of the total image. The reconstruction image can be viewed through an eyepiece or displayed on a television screen. During the last five years, improved method of fabricating optical fibers have led to a reduction in fiberscope diameter and an increase in the number of fibers, which in turn has increased resolution.

Optical fibers can also be used to deliver laser light. By use of laser beams, physicians can perform surgery inside the body, sometimes eliminating the need for invasive procedures in which healthy tissue must be cut through to reach the site of disease. Many of these procedures do not require anesthesia and can be performed in a physician's office. These technique have reduced the risk and the cost of medical care.

PASSAGE 2 – Questions 11-20

Many flower plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue the pollinator that the flower is full of far more pollen than neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flowers. Thus, the colored-coded communication system benefits both plants and insect.

For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-inidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. The the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiment with paper flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scene of the nectar.

In other types of plants, blossoms change from white to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.

PASSAGE 2 – Questions 11-20

Many flower plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue the pollinator that the flower is full of far more pollen than neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flowers. Thus, the colored-coded communication system benefits both plants and insect.

For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-inidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. The the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiment with paper flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scene of the nectar.

In other types of plants, blossoms change from white to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.

PASSAGE 2 – Questions 11-20

Many flower plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue the pollinator that the flower is full of far more pollen than neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flowers. Thus, the colored-coded communication system benefits both plants and insect.

For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-inidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. The the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiment with paper flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scene of the nectar.

In other types of plants, blossoms change from white to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.

PASSAGE 2 – Questions 11-20

Many flower plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue the pollinator that the flower is full of far more pollen than neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flowers. Thus, the colored-coded communication system benefits both plants and insect.

For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-inidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. The the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiment with paper flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scene of the nectar.

In other types of plants, blossoms change from white to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.

PASSAGE 2 – Questions 11-20

Many flower plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue the pollinator that the flower is full of far more pollen than neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flowers. Thus, the colored-coded communication system benefits both plants and insect.

For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-inidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. The the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiment with paper flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scene of the nectar.

In other types of plants, blossoms change from white to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.

PASSAGE 2 – Questions 11-20

Many flower plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue the pollinator that the flower is full of far more pollen than neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flowers. Thus, the colored-coded communication system benefits both plants and insect.

For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-inidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. The the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiment with paper flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scene of the nectar.

In other types of plants, blossoms change from white to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.

PASSAGE 2 – Questions 11-20

Many flower plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue the pollinator that the flower is full of far more pollen than neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flowers. Thus, the colored-coded communication system benefits both plants and insect.

For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-inidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. The the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiment with paper flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scene of the nectar.

In other types of plants, blossoms change from white to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.

PASSAGE 2 – Questions 11-20

Many flower plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue the pollinator that the flower is full of far more pollen than neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flowers. Thus, the colored-coded communication system benefits both plants and insect.

For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-inidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. The the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiment with paper flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scene of the nectar.

In other types of plants, blossoms change from white to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.

PASSAGE 2 – Questions 11-20

Many flower plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue the pollinator that the flower is full of far more pollen than neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flowers. Thus, the colored-coded communication system benefits both plants and insect.

For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-inidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. The the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiment with paper flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scene of the nectar.

In other types of plants, blossoms change from white to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.

PASSAGE 2 – Questions 11-20

Many flower plants woo insect pollinators and gently direct them to their most fertile blossoms by changing the color of individual flowers from day to day. Through color cues, the plant signals to the insect that it would be better off visiting one flower on its bush than another. The particular hue the pollinator that the flower is full of far more pollen than neighboring blooms. That nectar-rich flower also happens to be fertile and ready to disperse its pollen or to receive pollen the insect has picked up from another flowers. Thus, the colored-coded communication system benefits both plants and insect.

For example, on the lantana plant, a flower starts out on the first day as yellow, when it is rich with pollen and nectar. Influenced by an as-yet-inidentified environmental signal, the flower changes color by triggering the production of the pigment anthromyacin. It turns orange on the second day and red on the third. The the third day, it has no pollen to offer insects and is no longer fertile. On any given lantana bush, only 10 to 15 percent of the blossoms are likely to be yellow and fertile. But in tests measuring the responsiveness of butterflies, it was discovered that the insects visited the yellow flowers at least 100 times more than would be expected from haphazard visitation. Experiment with paper flowers and painted flowers demonstrated that the butterflies were responding to color cues rather than, say, the scene of the nectar.

In other types of plants, blossoms change from white to red, others from yellow to red, and so on. These color changes have been observed in some 74 families of plants.