Mars may once have been a very wet place. A large number of clues remain from an earlier era, billions of years ago, hinting that the Red Planet was host to great rivers, lakes and perhaps even an ocean. But some of the clues are contradictory—they don’t all fit together in a coherent (一致的) whole. Little wonder, then, that the fate of water on Mars is such a hotly debated topic.
　　 The reason for the intense interest in Martian water is simple: Without water, there can be no life as we know it. If it has been 3.5 billion years since liquid water was present on Mars, the chance of finding life there is remote. But if water is present on Mars now, however well hidden, life may be holding on in some protected place.
　　 Based on what we have observed so far, Mars today is a frozen desert. It’s too cold for liquid water to exist on its surface and too cold to rain. The planet’s atmosphere is also too thin to permit any significant amount of snowfall.
　　 Even if some internal heat source warmed the planet up enough for ice to melt, it wouldn’t yield liquid water. The Martian atmosphere is so thin that even if the temperature rose above the freezing point the ice would change directly to water vapor.
　　 New debates will undoubtedly emerge as data from Mars Global Surveyor is digested. In 2001, NASA will send a new orbiter to Mars to search for carbonates(碳酸盐). In 2003, NASA will send two devices to Mars to hunt for water’s traces in rocks and soil on the surface. But many questions about the history of water on Mars are likely to remain unanswered until samples are returned from the Red Planet for examination on Earth. “I think the sample return is what we want. And if we could get samples of things like this back on Earth, I think it would do an awful lot to help us understand what’s going on on Mars,”says Mike Carr, author of the book Water on Mars.
　　 1. When talking about water on Mars, the writer thinks that ________.
　　 A. all the clues are contradictory
　　 B. it is a small wonder
　　 C. the topic is not so interesting as expected
　　 D. it is naturally a hotly debated topic
　　 2. Scientists are so interested in Martian water because ________ .
　　 A. water means life
　　 B. water was present there in the past
　　 C. life has been found on the frozen desert
　　 D. finding life there is impossible
　　 3. To the best of our knowledge, which of the following is not true of Mars today?
　　 A. It's a frozen desert.
　　 B. There is no liquid water on it.
　　 C. There is a lot of ice on it.
　　 D. There is no snow on it.
　　 4. If ice on Mars melted, what would most likely appear as a result?
　　 A. Liquid water.
　　 B. Rain.
　　 C. Snowfall.
　　 D. Water vapor.
　　 5. What should be done to better understand the history of water on Mars?
　　 A. Analyzing the data from Mars Global Surveyor.
　　 B. Sending more devices to Mars.
　　 C. Obtaining samples from Mars for analysis.
　　 D. Learning more about the history of water on Mars.
　　 参考答案：1. D 2. A 3. C 4. D 5. C
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