1、2008 年 2 月美国托福英语考试（TOEFL）阅读真题精选及答案解析(总分：116.00，做题时间：150 分钟)一、READING(总题数：5，分数：116.00)Colonizing the Americas via the Northwest CoastIt has long been accepted that the Americas were colonized by a migration of peoples from Asia, slowly traveling across a land bridge called Beringia (now the Bering St
2、rait between northeastern Asia and Alaska) during the last Ice Age. The first water craft theory about the migration was that around 11,000-12,000 years ago there was an ice-free corridor stretching from eastern Beringia to the areas of North America south of the great northern glaciers. It was the
3、midcontinental corridor between two massive ice sheets-the Laurentide to the west-that enabled the southward migration. But belief in this ice-free corridor began to crumble when paleoecologist Glen MacDonald demonstrated that some of the most important radiocarbon dates used to support the existenc
4、e of an ice-free corridor were incorrect. He persuasively argued that such an ice-free corridor did not exist until much later, when the continental ice began its final retreat.Support is growing for the alternative theory that people using watercraft, possibly skin boats, moved southward from Berin
5、gia along the Gulf of Alaska and then southward along the Northwest Coast of North America possibly as early as 16,000 years ago. This route would have enabled humans to enter southern areas of the Americans prior to the melting of the continental glaciers. Until the early 1970s, most archaeologists
6、 did not consider the coast a possible migration route into the Americans because geologists originally believed that during the last Ice Age the entire Northwest Coast was covered by glacial ice. It had been assumed that the ice extended westward from the Alaskan/Canadian mountains to the very edge
7、 of the continental shelf, the flat, submerged part of the continent that extend into the ocean. This would have created a barrier of ice extending from the Alaska Peninsula, through the Gulf of Alaska and southward along the Northwest Coast of North America to what is today the state of Washington.
8、The most influential proponent of the coastal migration route has been Canadian archaeologist Knut Fladmark. He theorized that with the use of watercraft, people gradually colonized unglaciated refuges and areas along the continental shelf exposed by the lower sea level. Fladmarks hypothesis receive
9、d additional support from the fact that the greatest diversity in Native American languages occurs along the west coast of the Americans, suggesting that this region has been settled the longest.More recent geologic studies documented deglaciation and the existence of ice-free areas throughout major
10、 coastal areas of British Columbia, Canada, by 13,000 years ago. Research now indicates that sizable areas of southeastern Alaska along the inner continental shelf were not covered by ice toward the end of the last Ice Age. One study suggests that except for a 250-mile coastal area between southwest
11、ern British Columbia and Washington State, the Northwest Coast of North America was largely free of ice by approximately 16,000 years ago. Vast areas along the coast may have been deglaciated beginning around 16,000 years ago, possibly providing a coastal corridor for the movement of plants, animals
12、, and humans sometime between 13,000 and 14,000 years ago.The coastal hypothesis has gained increasing support in recent years because the remains of large land animals, such as caribou and brown bears, have been found in southeastern Alaska dating between 10,000 and 12,500 years ago. This is the ti
13、me period in which most scientists formerly believed the area to be inhospitable for humans. It has been suggested that if the environment were capable of supporting breeding populations of bears, there would have been enough food resources to support humans. Fladmark and others believe that the fir
14、st human colonization of America occurred by boat along the Northwest Coast during the very late Ice Age, possibly as early as 14,000 years ago. The most recent geologic evidence indicates that it may have been possible for people to colonize ice-free regions along the continental shelf that were st
15、ill exposed by the lower sea level between 13,000 and 14,000 ago.The coastal hypothesis suggests an economy based on marine mammal hunting, saltwater fishing gathering, and the use of watercraft. Because of the barrier of ice to the east, the Pacific Ocean to the west, and populated areas to the nor
16、th, there may have been a greater impetus for people to move in a southerly direction（分数：24）(1).According to paragraph 1, the theory that people first migrated to the Americans by way of an ice-free corridor was seriously called into question by（分数：2）A.paleoecologist Glen MacDonalds argument that th
17、e original migration occurred much later than had previously been believedB.the demonstration that certain previously accepted radiocarbon dates were incorrectC.evidence that the continental ice began its final retreat much later than had previously been believedD.research showing that the ice-free
18、corridor was not as long lasting as had been widely assumed(2).The word persuasively in the passage is closest in meaning to（分数：2）A.aggressivelyB.inflexiblyC.convincinglyD.carefully(3).Paragraph 2 begins by presenting a theory and then goes on to（分数：2）A.discuss why the theory was rapidly accepted bu
19、t then rejectedB.present the evidence on which the theory was basedC.cite evidence that now shows that the theory is incorrectD.explain why the theory was not initially considered plausible(4).The phrase prior to is closest in meaning to（分数：2）A.beforeB.immediately afterC.duringD.in spite of(5).Parag
20、raph 2 supports the idea that, before the 1970s, the most archaeologists held which of the following views about the earliest people to reach the Americas?（分数：2）A.They could not have sailed directly from Beringia to Alaska and then southward because, it was thought, glacial ice covered the entire co
21、astal region.B.They were not aware that the climate would continue to become milderC.They would have had no interest in migrating southward from Beringia until after the continental glaciers had begun to meltD.They lacked the navigational skills and appropriate boats needed long-distance trips(6).Wh
22、ich of the sentences below best expresses the essential information in the highlighted sentence in the passage? （分数：2）A.Because this region has been settled the longest, it also displays the greatest diversity in Native American languagesB.Fladmarks hypothesis states that the west coast of the Ameri
23、cas has been settled longer than any other region.C.The fact that the greatest diversity of Native American languages occurs along the west coast of the Americans lends strength to Fradmarks hypothesisD.According to Fladmark, Native American languages have survived the longest along the west coast o
24、f the Americas.(7).The authors purpose in paragraph 4 is to（分数：2）A.indicate that a number of recent geologic studies seem to provide support for the coastal hypothesisB.indicate that coastal and inland migrations may have happened simultaneouslyC.explain why humans may have reached Americas northwes
25、t coast before animals and plants didD.show that the coastal hypothesis may explain how people first reached Alaska but it cannot explain how people reached areas like modern British Columbia and Washington State(8).The word Vast in the passage is closest in meaning to（分数：2）A.FrozenB.VariousC.Isolat
26、edD.Huge(9).According to paragraph 5, the discovery of the remains of large land animals supports the coastal hypothesis by providing evidence that（分数：2）A.humans were changing their hunting techniques to adapt to coastal rather than inland environmentsB.animals had migrated from the inland to the co
27、asts, an indication that a midcontinental ice-free corridor was actually implausibleC.humans probably would have been able to find enough resources along the coastal corridorD.the continental shelf was still exposed by lower sea levels during the period when the southward migration of people began(1
28、0).The word inhospitable in the passage is closest in meaning to（分数：2）A.not familiarB.not suitableC.not dangerousD.not reachable(11).According to paragraph 5, the most recent geologic research provides support for a first colonization of America dating as far back as（分数：2）A.16,000 years agoB.14,000
29、years agoC.12,500 years agoD.10,000 years ago(12).The word impetus in the passage is closest in meaning to（分数：2）A.chanceB.protectionC.possibilityD.incentiveRunning Water on MarsPhotographic evidence suggests that liquid water once existed in great quantity on the surface of Mars. Two types of flow f
30、eatures are seen: runoff channels and outflow channels. Runoff channels are found in the southern highlands. These flow features are extensive systemssometimes hundreds of kilometers in total lengthof interconnecting, twisting channels that seem to merge into larger, wider channels. They bear a stro
31、ng resemblance to river systems on Earth, and geologists think that they are dried-up beds of long-gone rivers that once carried rainfall on Mars from the mountains down into the valleys. Runoff channels on Mars speak of a time 4 billion years ago (the age of the Martian highlands), when the atmosph
32、ere was thicker, the surface warmer, and liquid water widespread.Outflow channels are probably relics of catastrophic flooding on Mars long ago. They appear only in equatorial regions and generally do not form extensive interconnected networks. Instead, they are probably the paths taken by huge volu
33、mes of water draining from the southern highlands into the northern plains. The onrushing water arising from these flash floods likely also formed the odd teardrop-shaped “islands” (resembling the miniature versions seen in the wet sand of our beaches at low tide) that have been found on the plains
34、close to the ends of the outflow channels. Judging from the width and depth of the channels, the flow rates must have been truly enormousperhaps as much as a hundred times greater than the 105 tons per second carried by the great Amazon river. Flooding shaped the outflow channels approximately 3 bil
35、lion years ago, about the same times as the northern volcanic plains formed.Some scientists speculate that Mars may have enjoyed an extended early Period during which rivers, lakes, and perhaps even oceans adorned its surface. A 2003 Mars Global Surveyor image shows what mission specialists think ma
36、y be a deltaa fan-shaped network of channels and sediments where a river once flowed into a larger body of water, in this case a lake filling a crater in the southern highlands. Other researchers go even further, suggesting that the data provide evidence for large open expenses of water on the early
37、 Martian surface. A computer-generated view of the Martian north polar region shows the extent of what may have been an ancient ocean covering much of the northern lowlands. The Hellas Basin, which measures some 3,000 kilometers across and has a floor that lies nearly 9 kilometers below the basins r
38、im, is another candidate for an ancient Martian sea.These ideas remain controversial. Proponents point to features such as the terraced “beaches” shown in one image, which could conceivably have been left behind as a lake or ocean evaporated and the shoreline receded. But detractors maintain that th
39、e terraces could also have been created by geological activity, perhaps related to the geologic forces that depressed the Northern Hemisphere far below the level of the south, in which case they have nothing whatever to do with Martian water. Furthermore, Mars Global Surveyor data released in 2003 s
40、eem to indicate that the Martian surface contains too few carbonate rock layerslayers containing compounds of carbon and oxygenthat should have been formed in abundance in an ancient ocean. Their absence supports the picture of a cold, dry Mars that never experienced the extended mild period require
41、d to form lakes and oceans. However, more recent data imply that at least some parts of the planet did in fact experience long periods in the past during which liquid water existed on the surface.Aside from some small-scale gullies (channels) found since 2000, which are inconclusive, astronomers hav
42、e no direct evidence for liquid water anywhere on the surface of Mars today, and the amount of water vapor in the Martian atmosphere is tiny. Yet even setting aside the unproven hints of ancient oceans, the extent of the outflow channels suggests that a huge total volume of water existed on Mars in
43、the past. Where did all the water go? The answer may be that virtually all the water on Mars is now locked in the permafrost layer under the surface, with more contained in the planets polar caps.（分数：22）(1).The word merge in the passage is closest in meaning to（分数：2）A.expandB.separateC.straighten ou
44、tD.combine(2).What does the discussion in paragraph 1 of runoff channels in the southern highlands suggest about Mars?（分数：2）A.The atmosphere of Mars was once thinner than itB.Large amounts of rain once fell on parts of Mars.C.The river systems of Mars were once more extensive than Earths.D.The river
45、s of Mars began to dry up about 4 billion years ago.(3).The word relics in the passage is closest in meaning to（分数：2）A.remainsB.sitesC.requirementsD.sources(4).The word miniature in the passage is closest in meaning to（分数：2）A.temporaryB.smallC.multipleD.familiar(5).In paragraph 2, why does the autho
46、r include the information that 105 tons of water flow through the Amazon river per second?（分数：2）A.To emphasize the great size of the volume of water that seems to have flowed through Mars outflow channelsB.To indicate data used by scientists to estimate how long ago Mars outflow channels were formed
47、C.To argue that flash floods on Mars may have been powerful enough to cause tear-shaped “islands” to formD.To argue that the force of flood waters on Mars was powerful enough to shape the northern volcanic plains(6).According to paragraph 2, all of the following are true of the outflow channels on M
48、ars EXCEPT：（分数：2）A.They formed at around the same time that volcanic activity was occurring on the northern plains.B.They are found only on certain parts of the Martian surface.C.They sometimes empty onto what appear to have once been the wet sands of tidal beaches.D.They are thought to have carried
49、 water northward from the equatorial regions(7).All of the following questions about geological features on Mars are answered in paragraph 3 EXCEPT:（分数：2）A.What are some regions of Mars that may have once been covered with an ocean?B.Where do mission scientists believe that the river forming the delta emptied?C.Approximately how many craters on Mars do mission scientists believe may once have been lakes filled with water?D.During what period of Mars history do some scientists think it may have had large bodies of water?(8).According to paragraph 3, images of Mars surface hav
