托福阅读真题解析：火星上的流水

　　○But detractors argue that the terraces may have been formed by geological activity ratherthan by the presence of water.

　　○But detractors argue that the terraces may be related to geological forces in the NorthernHemisphere of Mars, rather than to Martian water in the south.

　　○But detractors argue that geological forces depressed the Northern Hemisphere so far belowthe level of the south that the terraces could not have been formed by water.

　　10. According to paragraph 4, what do the 2003 Global Surveyor data suggest About Mars?

　　○Ancient oceans on Mars contained only small amounts of carbon.

　　○The climate of Mars may not have been suitable for the formation of large bodies of water.

　　○Liquid water may have existed on some parts of Mars’ surface for long periods of time.

　　○The ancient oceans that formed on Mars dried up during periods of cold, dry weather.

　　Paragraph 5 Aside from some small-scale gullies (channels) found since2000, which areinconclusive, astronomers have no direct evidence for liquid water anywhere on the surfaceof Mars today, and the amount of water vapor in the Martian atmosphere is tiny. Yet evensetting aside the unproven hints of ancient oceans, the extent of the past. Where did all thewater go? The answer may be that virtually all the water on Mars is now locked in thepermafrost layer under the surface, with more contained in the planet’s polar caps.

　　11. The word hints in the passage is closest in meaning to

　　○clues

　　○features

　　○arguments

　　○effects

　　Paragraph 2 Outflow channels are probably relics of catastrophic flooding on Mars long ago.They appear only in equatorial regions and generally do not form extensive interconnectednetworks. Instead, they are probably the paths taken by huge volumes of water draining fromthe