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Passage 6

The Sun today is a yellow dwarf star. It is fueled by thermonuclear reactions near its centerthat convert hydrogen to helium. The Sun has existed in its present state for about 4 billion, 600million years and is thousands of times larger than Earth.
By studying other stars, astronomers can predict what the rest of the Sun’s life will be like.About 5 billon years from now, the core of the Sun will shrink and become hotter. The surfacetemperature will fall. The higher temperature of the center will increase the rate of thermonuclearreactions. The outer regions of the Sun will expand approximately 35 million miles, about thedistance to mercury, which is the closest planet to the Sun. The Sun will then be a red giant star.Temperatures on the Earth will become too hot for life to exist.
Once the Sun has used up its thermonuclear energy as a red giant, it will begin to shrink. After itshrinks to the size of the Earth, it wil
A. is approximately halfway through its life as a yellow dwarf
B. has been in existence for 10 billion years
C. is rapidly changing in size and brightness
D. will continue as a yellow dwarf for another 10 billion years

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Passage 6

The Sun today is a yellow dwarf star. It is fueled by thermonuclear reactions near its centerthat convert hydrogen to helium. The Sun has existed in its present state for about 4 billion, 600million years and is thousands of times larger than Earth.
By studying other stars, astronomers can predict what the rest of the Sun’s life will be like.About 5 billon years from now, the core of the Sun will shrink and become hotter. The surfacetemperature will fall. The higher temperature of the center will increase the rate of thermonuclearreactions. The outer regions of the Sun will expand approximately 35 million miles, about thedistance to mercury, which is the closest planet to the Sun. The Sun will then be a red giant star.Temperatures on the Earth will become too hot for life to exist.
Once the Sun has used up its thermonuclear energy as a red giant, it will begin to shrink. After itshrinks to the size of the Earth, it wil
A. To alert people to the dangers posed by the Sun.
B. To discuss conditions on Earth in the far future.
C. To present a theory about red giant stars.
D. To describe changes that the Sun will go through.

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The sun today is a yellow dwarf star. It is fueled by thermonuclear reactions near its center that convert hydrogen to helium. The sun has existed in its present state for about 4 billion, 600 million years and is thousands of times larger than the Earth.
By studying other stars, astronomers can predict what the rest of the sun’s life will be like. About 5 billion years from now, the core of the sun will shrink and become hotter. The surface temperature will fail. The higher temperature of the center will increase the rate of thermonuclear reactions. The outer regions of the sun will expand approximately 35 million miles, about the distance to mercury, which is the closest planet to the sun. The sun will then be a red giant star. Temperatures on the earth will become too hot for life to exist.
Once the sun has used up its thermonucle
A. Alarmed. B. Pessimistic. C. Comic. D. Objective.

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[单项选择]The sun today is a yellow dwarf star. It is fueled by thermonuclear reactions near its center that convert hydrogen to helium. The sun has existed in its present state for about 4 billion, 600 million years and is thousands of times larger than the Earth.
By studying other stars, astronomers can predict what the rest of the sun’s life will be like. About 5 billion years from now, the core of the sun will shrink and become hotter. The surface temperature will fail. The higher temperature of the center will increase the rate of thermonuclear reactions. The outer regions of the sun will expand approximately 35 million miles, about the distance to mercury, which is the closest planet to the sun. The sun will then be a red giant star. Temperatures on the earth will become too hot for life to exist.
Once the sun has used up its thermonuclear energy as a red giant, it will begin to shrink. After it shrinks to the size of the earth, it will become a white dwarf star. The sun m
A. To alert people to the dangers posed by the sun.
B. To discuss conditions on earth in the far future.
C. To present a theory about red giant stars.
D. To describe changes that the sun will go through.

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The sun today is a yellow dwarf star. It is {{U}}fueled{{/U}} by thermonuclear reactions near its center that convert hydrogen to helium. The sun has existed in its present state for about 4 billion, 600 million years and is thousands of times larger than the Earth.
By studying other stars, astronomers can predict what the rest of the sun’s life will be like. About 5 billion years from now, the core of the sun will shrink and become hotter. The surface temperature will fail. The higher temperature of the center will increase the rate of thermonuclear reactions. The outer regions of the sun will expand approximately 35 million miles, about the distance to mercury, which is the closest planet to the sun. The sun will then be a red giant star. Temperatures on the earth will become too hot for life to exist.
Once the sun has used up its t
A. the same size as the planet Mercury
B. thousands of times smaller than it is today
C. around 35 million miles in diameter
D. cold and dark

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