托福阅读真题解析：火星上的流水

　　7. All of the following questions about geological features on Mars are answered in paragraph 3EXCEPT:

　　○What are some regions of Mars that may have once been covered with an ocean?

　　○Where do mission scientists believe that the river forming the delta emptied?

　　○Approximately how many craters on Mars do mission scientists believe may once have beenlakes filled with water?

　　○During what period of Mars’ history do some scientists think it may have had large bodies ofwater?

　　8. According to paragraph 3, images of Mars’ surface have been interpreted as support for theidea that

　　○the polar regions of Mars were once more extensive than they are now

　　○a large part of the northern lowlands may once have been under water

　　○deltas were once a common feature of the Martian landscape

　　○the shape of the Hellas Basin has changed considerably over time

　　Paragraph 4 These ideas remain controversial. Proponents point to features such as theterraced “beaches” shown in one image, which could conceivably have been left behind as a lakeor ocean evaporated and the shoreline receded. But detractors maintain that the terraces couldalso have been created by geological activity, perhaps related to the geologic forces thatdepressed the Northern Hemisphere far below the level of the south, in which case they havenothing whatever to do with Martian water. Furthermore, Mars Global Surveyor data released in2003 seem to indicate that the Martian surface contains too few carbonate rock layers―layerscontaining compounds of carbon and oxygen―that should have been formed in abundance inan ancient ocean. Their absence supports the picture of a cold, dry Mars that neverexperienced the extended mild period required to form lakes and oceans. However, morerecent data imply that at least some parts of the planet did in fact experience long periods inthe past during which liquid water existed on the surface.

　　9. Which of the sentences below best expresses the essential information in the highlightedsentence in the passage? Incorrect choices change the meaning in important ways or leave outessential information.

　　○But detractors argue that geological activity may be responsible for the water associated withthe terraces.