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  3. Life in the Universe Many scientists today are convinced that life exists elsewhere in the universe-life probably much like

Life in the Universe Many scientists today are convinced that life exists elsewhere in the universe-life probably much like

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问题                         Life in the Universe
    Many scientists today are convinced that life exists elsewhere in the universe-life probably much like that on our own planet. They reason in the following way.
    As far as astronomers can determine, the entire universe is built of the same matter. They have no reason to doubt that matter obeys the same laws in every part of the universe. Therefore, it is reasonable to guess that other stars, with their own planets, were born in the same way as our own solar system. What we know of life on earth suggests that life will arise wherever the proper conditions exist.
    Life requires the right amount and kind of atmosphere. This eliminates all those planets in the universe that are not about the same size and weight as the earth. A smaller planet would lose its atmosphere; a larger one would hold too much of it.
    Life also requires a steady supply of heat and light. This eliminates double stars, or stars that flare up suddenly. Only single stars that are steady sources of heat and light like our sun would qualify.
    Finally, life could evolve only if the planet is just the right distance from its sun. With a weaker sun than our own, the planet would have to be closer to it. With a stronger sun, it would have to be farther away.
    If we suppose that every star in the universe has a family of planets, then how many planets might support life? First, eliminate those stars that are not like our sun. Next eliminate most of their planets; they are either too far from or too close to their suns. Then eliminate all those planets which are not the same size and weight as the earth. Finally, remember that the proper conditions do not necessarily mean that life actually does exist on a planet. It may not have begun yet, or it may have already died out.
    This process of elimination seems to leave very few planets on which earthlike life might be found. However, even if life could exist on only one planet in a million, there are so many billions of planets that this would still leave a vast number on which life could exist.
At the end of the passage the author suggests that______.
选项 A、it is impossible for life to exist on planets
B、earthlike life could only exist on a few planets
C、life could exist on only one planet in a million
D、life could exist on a great number of planets
答案D
解析 推断题。最后一段中：This process of elimination seems to leave very few planets on which earthlike life might be found．However, even if life could exist on only one planet in a million, there are SO many billions of planets that this would still leave a vast number on which life could exist．虽然第一句似乎是在说earthlike life could only exist on a few planets, 即B选项的内容, 但是马上用However一转折, 用来强调后面的内容, 即：即使一百万个行星中有一个行星上存在生命, 但宇宙中有无数的数以十亿计的行星, 这样的话, 仍有相当大数量的行星上可能存在生命。这个和D选项内容一致。
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