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  3. As NASA prepares to set twin robots loose on the Martian surface and makes plans to send another in 2007, the agency’s long term

As NASA prepares to set twin robots loose on the Martian surface and makes plans to send another in 2007, the agency’s long term

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问题     As NASA prepares to set twin robots loose on the Martian surface and makes plans to send another in 2007, the agency’s long term goal is clear: determine whether the red planet does or ever did harbor life.
    But the current search for life is necessarily limited to life as we know it, organisms dependent on liquid water. A SPACE, com reader recently suggested that "We as humans are arrogant, simply believing that any other form of life will be just like us. "     Researchers devoted to the search for extraterrestrial(ET)have a similar view. "Scientists’ approach to finding life is very Earth-centric," says Kenneth Nealson, a geobiologist at the University of Southern California. "Based on what we know about life on Earth, we set the limits for where we might look on other planets," Nealson said. Within that framework, however, there are extreme cases of life on Earth that suggest the range of places to look on frigid Mars.
    Nealson and his colleagues recently found the most extreme sort of organism in a salty liquid lake under the permafrost of Siberia. The organism, named cryopegella, can exist at colder temperatures than any previously discovered. Nealson’s team figures that if the ice at the polar caps of Mars warmed to liquid water, organisms like cryopegella could have awakened and repaired any damage that might have occurred to their various cellular components. That does not mean there are necessarily dormant microbes within the ice caps of Mars. But it does suggest a broader range of potential cradles for life.
    Other researchers agree, and a host of so-called "extremophile" discoveries on Earth in recent years indicate the polar regions of Mars might be prime hunting grounds. As on Earth, organisms there might be slathered in natural antifreeze or be able to go dormant for tens of thousands of years, waiting for a brief thaw, their moment in the Sun.
    Meanwhile, scientists recognize that there could indeed be life elsewhere in the universe that does not require water. And some astrobiologists are trying to explore the possibilities. But it is a tough problem to approach. In looking for "life as we don’t know it," it’s hard to even imagine what to expect.
    Life might or might not exist on Mars. If there are critters there, they might or might not be like bacteria on Earth. In laboratory conditions, scientists in 2001 were able to get one-celled organisms to incorporate an amino acid—a fundamental building block of life—that no other known life uses. The discovery borders on the creation of artificial life, experts said. It also suggests that ET might operate by entirely different rules than those we’re used to.
    If life on Mars is fundamentally different from what scientists understand life to be, then current spacecraft and others in the works may well not recognize what’s right under their mechanical noses.
The purpose of the author mentioning scientists’ laboratory creation in 2001 is to emphasize the idea that .
选项 A、it is hard to imagine what ET is really like
B、life might or might not exist on Mars
C、it is possible to create artificial life
D、Martians may live by entirely different rules
答案D
解析 综合理解题。文章在倒数第二段提到了科学家2001年的实验室实验。在该实验中，科学家们能使一种单细胞生物体合成一种氨基酸，这种氨基酸是构建生命的基本单位，但任何已知的其他生命都不使用它。专家说，这一发现揭开了创造人工生命的序幕，但也暗示外星人存在的方式可能与我们所习惯了的完全不同，也就是说有一些生命形式与我们人类所知的是不同的。由于本文主要是讲外星人可能存在于我们人类假设的范围之外，因此作者用2001年这个实验的例子是为了进一步强调这一点，而不是为了强调人工创造生命的可能性，故D是正确答案。
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