托福阅读真题解析：火星上的流水

　　1. The word merge in the passage is closest in meaning to

　　○expand

　　○separate

　　○straighten out

　　○combine

　　2. What does the discussion in paragraph 1 of runoff channels in the southern highlandssuggest about Mars?

　　○The atmosphere of Mars was once thinner than it is today.

　　○Large amounts of rain once fell on parts of Mars.

　　○The river systems of Mars were once more extensive than Earth’s.

　　○The rivers of Mars began to dry up about 4 billion years ago.

　　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 southern highlands into the northern plains. The onrushing water arising from these flashfloods likely also formed the odd teardrop-shaped “islands” (resembling the miniature versionsseen in the wet sand of our beaches at low tide) that have been found on the plains close tothe ends of the outflow channels. Judging from the width and depth of the channels, the flowrates must have been truly enormous―perhaps as much as a hundred times greater than the105 tons per second carried by the great Amazon river. Flooding shaped the outflow channelsapproximately 3 billion years ago, about the same times as the northern volcanic plainsformed.

　　3. The word relics in the passage is closest in meaning to

　　○remains

　　○sites

　　○requirements

　　○sources

　　4. The word miniature in the passage is closest in meaning to

　　○temporary

　　○small

　　○multiple

　　○familiar