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  3. NASA’s new Mars probe, a $ 2. 5 billion, nuclear-powered rover the size of a small car, is at the Florida launch site being prep

NASA’s new Mars probe, a $ 2. 5 billion, nuclear-powered rover the size of a small car, is at the Florida launch site being prep

admin2019-06-10  16
问题    NASA’s new Mars probe, a $ 2. 5 billion, nuclear-powered rover the size of a small car, is at the Florida launch site being prepared for its nine-month journey to the red planet, with one key issue still unresolved — where to land.
   The Mars Science Laboratory, nicknamed Curiosity, will delve deeper than any previous science mission to answer the age-old question about whether there is life beyond Earth. The goal of the project is to determine if the region where Curiosity lands has or ever had the right conditions to support microbial life.
   Scientists spent years poring over pictures and analyzing chemical data collected by a fleet of robotic spacecraft circling Mars before narrowing down the options to four finalists; Eberswalde Crater, Mawrth Vallis, Holden Crater and Gale Crater.
   " Each site has things that make it good and things that make it not quite so good," said planetary scientist Matt Golombek. " It’s kind of hard to select because it boils down to which kind of science is important to you, and that’s almost personal.
   The rover will touch down within a 12. 4-by-15. 5 mile targeted area, a relatively small patch of real estate for interplanetary travel. Being able to make a precision touchdown hasn’t made things easy for scientists tapped to choose Curiosity’s landing spot. In the past, lots of scientifically interesting sites were eliminated because of concerns the spacecraft wouldn’t be able to make a safe landing.
   Eberswalde Crater stands out among the four contenders because of a single, stunning geologic feature -— a delta, believed to be a buildup of sediment left by flowing water.
   " If you want a site that probably has the highest chance of preserving organics and biosignatures that might have existed, this is the place," Golombek said. " It’s just a spectacular example where water came and built up a sediment. "
   The attractive Eberswalde site, however, has a serious drawback as well. If its deposits turn out to be nothing more than clay-dusted rocks, the mission would be largely a bust.
   The next candidate site, Mawrth Vallis, is an open book of Martian history, with exposed valley walls that date back about 3.7 billion years, nearly as old as the planet itself. Its clays, known as phyllosilicates, form in the presence of water, believed to be a necessary ingredient for life. Mawrth’s short-coming is that scientists don’t understand how it formed. Water that once flowed in the valley could have been far too acidic for life to flourish.
The passage will probably continue with the description of______.
选项 A、other key ingredients for life besides water
B、Holden Crater and Gale Crater respectively
C、scientists’ further analysis of Mawrth Vallis
D、different difficulties in making the decision
答案B
解析 本题是文章结构题，考查整篇文章的行文脉络。另外，第三段最后一行中提到四个环形山，本文已经讨论了前两个，很可能接下来要提到后两个。
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