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  3. Now that we are fairly sure that there are many Earth-like planets in the Galaxy, the time is ripe (or almost so) to wonder whet

Now that we are fairly sure that there are many Earth-like planets in the Galaxy, the time is ripe (or almost so) to wonder whet

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问题     Now that we are fairly sure that there are many Earth-like planets in the Galaxy, the time is ripe (or almost so) to wonder whether these new worlds do indeed have a high probability of hosting new forms of life.
    Currently, the best【C1】________on the existence of other planets comes from NASA’s【C2】________Kepler satellite, which has been mapping an area of the sky【C3】________some 150,000 stars.
    Scientists estimate that around 5 percent of planets in our galaxy have masses similar【C4】________Earth’s and, possibly, are within the habitable zone of their stars, meaning that【C5】________they hold water it has a high chance of being liquid.【C6】________there are about 200 billion stars in our galaxy alone, scientists estimate that there should be about 10 billion Earth-size planets. Not bad, especially if we【C7】________that to be Earth-size and within a habitable zone is all it takes for life to take hold in an【C8】________world. In practice, however, the situation is much more【C9】________, since it depends on what life is and how it appears in a planet,【C10】________on the planet’s detailed geological history.
    Here on Earth life appeared some 3.5 billion years ago. 11 that it may have been here as far【C12】________as 3.8 billion years ago remain tentative. For about the first three billion years, life on earth was【C13】________in the form of single-cell creatures. Only when Earth’s atmosphere was full of oxygen did more sophisticated organisms appear.
    【C14】________its unusual atmosphere, Earth’s heavy, single moon, its magnetic field also did something else that allowed complex life to【C15】________on its surface,【C16】________these, Complex life would find it very hard to【C17】________and survive.
    The results from Kepler’s mission are encouraging and exciting. We have the【C18】________of confirming the existence of countless other worlds out there. Based on these findings, we should indeed【C19】________that other worlds would host some kind of simple life. However, as some scientists argued, Earth and its ability to host complex life will probably remain a【C20】________phenomenon in this and other galaxies.
【C18】
选项 A、risk
B、liberty
C、privilege
D、objective
答案C
解析 该段第一句谈到来自开普勒太空望远镜项目的结果令人鼓舞和振奋。正是因为开普勒太空望远镜和它所提供的资料，我们才能享有这样的殊荣去求证地外世界的存在。C项privileges“特权，殊荣”符合上下文语义。开普勒太空望远镜的资料和发现应当能提供“确认外星世界存在”的机会和优势。而不应使得我们有证实此事的“风险”(A项risk)和“自由”(B项liberty)。这些研究结果也不会为我们提供 “确认外星世界存在”的目标(D项objective)。
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