2. 外语
  3. Perhaps more than anything else, scientists are eager to find out if Martian life existed in the past—or still exists.【C1】______

Perhaps more than anything else, scientists are eager to find out if Martian life existed in the past—or still exists.【C1】______

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问题    Perhaps more than anything else, scientists are eager to find out if Martian life existed in the past—or still exists.【C1】______telescopes first zoomed【C2】______Mars in the 17th century, people have conjured up a wild【C3】______of images or what Martians might look like. But space probes like the 1997 Sojourner land rover have yielded no evidence of such alien beings.
   Most experts agree that if life did at one time evolve on Mars, finding evidence of that life— which would likely take the form of tiny organisms—won’ t be easy.【C4】______, many scientists are optimistic. " We’ ve got organisms on Earth that adapted to life deep【C5】______the surface in underground water wells, "says Stephen Clifford.【C6】______life like that evolved on Mars four billion years ago, there’ s no reason why it【C7】______today. "
  【C8】______last year’ s disappointing losses, the future of Martian exploration looks【C9】______This year, two major films about fictitious Mars missions—Red Planet and Missions to Mars—are certain to heighten interest in our planetary neighbour. More important, plans for new sets of NASA orbiters and landers—one to launch in 2001 , the other in 2003—are already in the works. Without a doubt, each new mission will inch scientists closer to【C10】______the mysteries of planet Mars.
【C6】
选项 A、When
B、What
C、That
D、If
答案D
解析 本题考查从句的引导词。when表示“当……之时”；what表示“什么”。that引导从句，没有实际意思。if表示“如果”，引导条件状语从句。根据句意，本题选D。
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