单选题
Mars Probe Watches Water-ice Fade

The pictures acquired by a NASA orbiter(卫星) show white material exposed by flesh meteorite impacts fading over time-behaviour expected of ice on Mars. An onboard instrument also detected the tell-tale chemical signature of water.
To date, exposed water-ice has only been seen at very high latitudes. The US space agency's (NASA) recent Phoenix probe famously dug into water-ice at its" high Arctic" landing site. The implication, even with the small set of examples scientists now have, is that broad deposits of ice sit just below the red top-soil of Mars. "There's a consistent picture starting to emerge now that these broad sheets may be common on Mars," observed Shane Byme of the University of Arizona, a member of the team running the HiRISE camera on NASA's Mars Reconnaissance Orbiter (MRO).
"The volume of water is probably comparable to the volume that we would have in the Greenland ice sheet on the Eanh-in the buried ice deposits that stretch from each pole to mid-latitudes. "
MRO has produced" earlier" and" later" images at five fresh impact sites made in 2008. These were all halfway between the North Pole and the equator on Mars.
The craters (环形山, 陨石坑) were small, just a few metres across, gouged out by incoming space rocks that may have been no more than 10cm in size. The bright, white deposits uncovered by the impacts were seen to wither over time, something exposed water-ice cannot help but do in the low-pressure Martian atmosphere. It is bound to sublimate-to tum directly from a solid into a Vapour.
However, the length of time it took to fade was a good indication that the ice was very pure. Had it contained a lot of dirt mixed in with it, the ice would have sublimated much quicker, scientists said.
The discoveries made by MRO are said to indicate that Mars had a more humid climate in the relatively recent past, within the last 10,000 years. Scientists suspect much of this ice came out of the atmosphere. Water vapour in the atmosphere will diffuse through the particles of the soil until it gets to a certain depth where it then freezes.
The locations of the exposed ice fit with the models used to predict where ground ice might be stable, i. e. from mid up to high latitudes.
"The more humid the Martian atmosphere, the more extensive the area of this stable ice. " explained Shane Byme. "Based on the locations of these craters, we are able to say something about how much water was in the Martian atmosphere recently, and that turns out to be a lot more than is in the atmosphere today—maybe almost double what's in the atmosphere today. /

单选题 What new findings has NASA acquired?
【正确答案】 C
【答案解析】The pictures acquired by a NASA orbiter(卫星)show white material fading over time -behaviour expected of ice on Mars. The US space agency's (NASA) recent Phoenix probe Famously dug into Water-ice at its "high Arctic" landing site. 由文章第一段以及第二段我们可以得知：一颗美国宇航局卫星获得的图片显示由于新的陨石撞击而外露出的白色物质正随着时间的流逝而消失，凤凰号探测器在火星北极高纬度着陆时恰好插入水冰，虽然这些例子不多，但已经暗示了就在火星表层土下藏有大量的冰块。所以本题正确答案为C。
单选题 Where has the exposed water-ice been seen to date?
【正确答案】 D
【答案解析】由题干关键词“exposed water-ice”和“to date”定位到第二段第一句：To date. exposed water-ice has only been seen at very high latitudes(迄今为止，只有在非常高纬度区域发现外露的水冰)。可见，本题正确答案为D。
单选题 Why did scientist say the ice was very pure?
【正确答案】 B
【答案解析】文章第五段的大意为：从融化的时间长短可以判断冰块非常的纯净，科学家说，含有污物的冰块融化更快(Had it contained a lot of dirt mixed in with it, the ice would have sublimated much quicker)。反之，冰越纯净，融化的速度就越慢。所以此题B为正确答案。
单选题 Which of the following is true according to Shane Byme?
【正确答案】 A
【答案解析】由题干关键词Shane Byrne定位到第二段第四句："There's a consistent picture starring to emerge now that these broad sheets may be common on Mars" observed Shane Byrne of the University of Arizona(亚利桑那州人学的Shane Byrne说这张一致的图片开始显示出一个事实，那就是这些人片冰块在火星可能很常见)，选项A与之相符，所以正确答案为A。
单选题 What did the MRO's discoveries indicate?
【正确答案】 A
【答案解析】由题干关键词“discovers”和“indicate”定位到第六段第一句：The discoveries made by MRO are said to indicate that Mars had a more humid climate in the relatively recent past, within the last 10,000 years(美国宇航局火星侦察卫星的发现显示出火星近一万年的气候比较潮湿)。可见，该题的正确答案为A。