托福阅读真题解析：火星上的流水

　　5. In paragraph 2, why does the author include the information that 105 tons of water flowthrough the Amazon river per second?

　　○To emphasize the great size of the volume of water that seems to have flowed through Mars’outflow channels

　　○To indicate data used by scientists to estimate how long ago Mars’ outflow channels wereformed

　　○To argue that flash floods on Mars may have been powerful enough to cause tear-shaped“islands” to form

　　○To argue that the force of flood waters on Mars was powerful enough to shape the northernvolcanic plains

　　6. According to paragraph 2, all of the following are true of the outflow channels on MarsEXCEPT:

　　○They formed at around the same time that volcanic activity was occurring on the northernplains.

　　○They are found only on certain parts of the Martian surface.

　　○They sometimes empty onto what appear to have once been the wet sands of tidal beaches.

　　○They are thought to have carried water northward from the equatorial regions.

　　Paragraph 3 Some scientists speculate that Mars may have enjoyed an extended early Periodduring which rivers, lakes, and perhaps even oceans adorned its surface. A 2003 Mars GlobalSurveyor image shows what mission specialists think may be a delta―a fan-shaped network ofchannels and sediments where a river once flowed into a larger body of water, in this case a lakefilling a crater in the southern highlands. Other researchers go even further, suggesting thatthe data provide evidence for large open expenses of water on the early Martian surface. Acomputer-generated view of the Martian north polar region shows the extent of what may havebeen an ancient ocean covering much of the northern lowlands. The Hellas Basin, whichmeasures some 3,000 kilometers across and has a floor that lies nearly 9 kilometers below thebasin’s rim, is another candidate for an ancient Martian sea.