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  3. The sun today is a yellow dwarf star. It is fueled by thermonuclear reaction

The sun today is a yellow dwarf star. It is fueled by thermonuclear reaction

游客2023-12-27  16
问题     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 may throw off huge amounts of gases in violent eruptions called nova explosions as it changes from a red giant to a white dwarf.
    After billions of years as a white dwarf, the Sun will have used up all its fuel and will have lost its heat. Such a star is called a black dwarf. After the Sun has become a black dwarf, the earth will be dark and cold. If any atmosphere remains there, it will have frozen onto the earth’s surface. [br] It can be inferred from the passage that the sun ______ .
选项 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
答案 A
解析 推断题型从文章第二段第一句得知，天文学家通过研究其它星球，能够预测太阳的余生/未来会是什么样子。文章没有谈及太阳已存在了多少年，选项B不对；尽管文章谈了太阳所要经历的变化，但这一过程是极其缓慢的，选项C也不对；文章第二段提到：距今大约五十亿年后，太阳的核会缩小并且会变得更热，而太阳表面的温度会降低，然后太阳将会成为一个红色的巨星，因此选项D也不对；所以A为答案。
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