托福-练习四及答案解析.doc

1、托福-练习四及答案解析(总分：38.00，做题时间：90 分钟)一、Passage 1(总题数：1，分数：12.00)LichensTo be certain, a lichen is not the most conspicuous of plants. Lichens grow in unassuming fashion on rocks, logs and other exposed surfaces in a wide range of habitats around the world. To the untrained eye they look like little more

2、than crusty patches that, at first glance, might easily be mistaken for a discoloration of the surface. Even if the average person should happen to notice the lichens presence and correctly identify it as some form of life, he is unlikely to go much further in contemplating it. Though almost totally

3、 ignored by the layperson, for the botanist, lichens are one of the most fascinating of all plants, and one of the most intensely studied.They are the subject of so much scientific scrutiny primarily because a lichen is not just one plant. It is, in fact, a composite organism made up of fungus and a

4、lgae living together in a close association that is, presumably, beneficial to both. When these two very different plants combine, the result is a unique and very long-lived composite organism that appears, at least on a macroscopic scale, to be a unitary plant. It is an organism that bears no resem

5、blance to either of its constituents when they are observed individually. The separate fungal and algae elements can be recognized only when the body of the plant, called a thallus because there are no stems or roots, is sectioned and examined under a microscope. When viewed this way, the fungus com

6、ponent dominates the picture, as it accounts for nine tenths of the total body mass of the lichen. But, entrapped within it, clearly visible as dark spots, are the algae cells. Essentially, nothing is known of how an amorphous mass of fungi and algae come together to form a highly differentiated, st

7、ructurally stable body.Despite all the scientific scrutiny lichens have received, it is still not entirely certain what each member gains from the association. Some researchers have speculated that the fungi join in the relationship because they are able to consume the algae cells as they die and th

8、erefore are guaranteed a food supply. It is well-known that the chlorophyll- containing algae cells produce food by means of photosynthesis. （分数：12.00）(1).According to paragraph 1 of the passage, which of the following statements is true?A. Very little is known about the internal structure of lichen

9、.B. The true nature of lichen is not readily apparent.C. Lichen is the only composite plant known to exist.D. Lichen is a very well-understood kind of plant.（分数：1.00）A.B.C.D.(2).The word “scrutiny“ in paragraph 2 is closest in meaning to _.A. observation B. harvesting C. understanding D. reverence（分

10、数：1.00）A.B.C.D.(3).The word “amorphous“ in paragraph 2 is closest in meaning to _.A. organized B. integrated C. composite D. formless（分数：1.00）A.B.C.D.(4).According to the passage, how might the fungus benefit from its association with algae? _A. The algae help provide it with necessary moisture.B. I

11、t consumes nutrients produced by algae.C. It is made less visible because of the algaes green color.D. The algae provide structural support.（分数：1.00）A.B.C.D.(5).Which of the following question is addressed in paragraph 3 of the passage?A. How long are lichens able to live?B. How do lichens reproduce

12、?C. How might algae benefit from the relationship with the fungus?D. How did the relationship between algae and fungus develop?（分数：1.00）A.B.C.D.(6).The word “retention“ in paragraph 3 is closest in meaning to _.A. consumption B. preservationC. combination D. generation（分数：1.00）A.B.C.D.(7).What is ma

13、in function of paragraph 4?A. To highlight the robust nature of lichens.B. To show how sensitive lichens are to environmental change.C. To describe the importance of lichens to environment.D. To explain why lichens are so widespread.（分数：1.00）A.B.C.D.(8).Which of the following if proven true would do

14、 most to clarify how fungus benefits from its association with algae?A. Sulfur dioxide prevents the fungus from absorbing the products of photo-synthesis.B. Sulfur dioxide tolerant species of lichen exist.C. Sulfur dioxide destroys the structure of the thallus.D. Sulfur dioxide kills only the algae

15、part of the lichen.（分数：1.00）A.B.C.D.(9).The word “susceptible“ in paragraph 5 is closest in meaning to _.A. resistant B. vulnerable C. impervious D. impermeable（分数：1.00）A.B.C.D.(10).Which is of the following is implied in paragraph 5 of the passage?A. Lichens will never return to large urban areas.B

16、. Many species of lichen are endangered.C. Large urban areas are serious polluted.D. Sulfur dioxide pollution in urban areas is declining.（分数：1.00）A.B.C.D.(11).Look at the four squares, , , and （分数：1.00）A.B.C.D.(12).Directions: An introductory sentence for a brief summary of the passage is provided

17、below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.The

18、passage tells the readers some knowledge about lichens._Answer ChoicesA. Lichens are not unitary organisms.B. Lichens live in a narrow range of habitats.C. Lichens are not typical of most plants.D. Lichens are well understood by botanists.E. Lichens are useful for studies of pollution.（分数：1.00）填空项 1

19、:_二、Passage 2(总题数：1，分数：13.00)Rising Sea LevelsPerhaps the most pervasive climatic effect of global warming is rapid escalation of ice melt. Mount Kilimanjaro in Africa, portions of the South American Andes, and the Himalayas will very likely lose most of their glacial ice within the next two decades

20、, affecting local water resources. Glacial ice continues its retreat in Alaska. NASA scientists determined that Greenlands ice sheet is thinning by about 1 m per year. The additional meltwater, especially from continental ice masses and glaciers, is adding to a rise in sea level worldwide. Satellite

21、 remote sensing is monitoring global sea level, sea ice, and continental ice. Worldwide measurements confirm that sea level rose during the last century.Surrounding the margins of Antarctica, and constituting about 11% of its surface area, are numerous ice shelves, especially where sheltering inlets

22、 or bays exist. Covering many thousands of square kilometers, these ice shelves extend over the sea while still attached to continental ice. The loss of these ice shelves does not significantly raise sea level, for they already displace seawater. The concern is for the possible surge of grounded con

23、tinental ice that the ice shelves hold back from the sea.Although ice shelves constantly break up to produce icebergs, some large sections have recently broken free. In 1998 an iceberg (150 km by 35 km) broke off the Ronne Ice Shelf, southeast of the Antarctic Peninsula. In March 2000 an iceberg tag

24、ged B-15 broke off the Ross Ice Shelf (some 90 longitude west of the Antarctic Peninsula), measuring 300 km by 40 kin. Since 1993, six ice shelves have disintegrated in Antarctica. About 8,000 km of ice shelf are gone, changing maps, freeing up islands to circumnavigation, and creating thousands of

25、icebergs. The Larsen Ice Shelf, along the east coast of the Antarctic Peninsula, has been retreating slowly for years. Larsen-A suddenly disintegrated in 1995. In only 35 days in early 2002, Larsen-B collapsed into icebergs. This ice loss is likely a result of the 2.5 temperature increase in the reg

26、ion in the last 50 years. In response to the increasing warmth, the Antarctic Peninsula is sporting new vegetation growth, previously not seen there.A loss of polar ice mass, augmented by melting of alpine and mountain glaciers (which experienced more than a 30 % decrease in overall ice mass during

27、the last century) will affect sea-level rise. The IPCC assessment states that “between one-third to one-half of the existing mountain glacier mass could disappear over the next hundred years“. Also, “there is conclusive evidence for a worldwide recession of mountain glaciers. This is among the clear

28、est and best evidence for a change in energy balance at the Earths surface since the end of the 19th century. “Sea-level rise must be expressed as a range of values that are under constant reassessment. The 2001 IPCC forecast for global mean sea-level rise this century, given regional variations, is

29、 from 0.110.88 m. The median value of 0.48 m is two to four times the rate of previous increase. These increases would continue beyond 2100 even if greenhouse gas concentrations are stabilized. （分数：13.00）(1).The word “confirm“ in the passage is closest in meaning to _.A. clarify B. prove C. assume D

30、. predict（分数：1.00）A.B.C.D.(2).There is more new plant life in Antarctica recently because _.A. the mountain glaciers have meltedB. the land masses have split into islandsC. the icebergs have broken into smaller piecesD. the temperature has risen by a few degrees（分数：1.00）A.B.C.D.(3).It may be inferre

31、d from this passage that icebergs are formed _.A. by a drop in ocean temperaturesB. when an ice shelf breaks freeC. from intensely cold islandsD. if mountain glaciers melt（分数：1.00）A.B.C.D.(4).The word “there“ in the passage refers to _.A. polar ice mass in the last 50 yearsB. the temperature increas

32、eC. new vegetation growthD. in the Antarctic Peninsula（分数：1.00）A.B.C.D.(5).In paragraph 4, the author explains the loss of polar and glacial ice by _.A. stating an educated opinionB. referring to data in a studyC. comparing sea levels worldwideD. presenting his research（分数：1.00）A.B.C.D.(6).The word

33、“conclusive“ in the passage is closest in meaning to _.A. definite B. independent C. unique D. valuable（分数：1.00）A.B.C.D.(7).The word “range“ in the passage is closest in meaning to _.A. function B. scale C. version D. lack（分数：1.00）A.B.C.D.(8).Why does the author mention the Scripps Institute of Ocea

34、nography in paragraph 6?A. The location near the coast endangers the Scripps facility.B. Research at Scripps indicates that the ocean is getting warmer.C. One quarter of the rising sea levels has been recorded at Scripps.D. Records at Scripps have been kept for nearly one hundred years.（分数：1.00）A.B.

35、C.D.(9).Which of the sentences below best expresses the information in the highlighted statement in the passage? The other choices change the meaning or leave out important information.A. Global warming on the surface of the planet may have been retarded during the last hundred years because heat in

36、 the atmosphere was absorbed by the oceans.B. Global warming on the surface of the ocean was greater than it was on the rest of the planet during the past century because of heat in the atmosphere.C. Too much heat in the atmosphere has caused global warming on the surface of the planet for the past

37、hundred years in spite of the moderation caused by the oceans.D. There is less heat being absorbed by the oceans now than there was a hundred years ago before the atmosphere began to experience global warming.（分数：1.00）A.B.C.D.(10).According to paragraph 7, why will people move away from the coastlin

38、es in the future?A. It will be too warm for them to live there.B. The coastlines will have too much vegetation.C. Flooding will destroy the coastal areas.D. No agricultural crops will be grown on the coasts.（分数：1.00）A.B.C.D.(11).Which of the following statements most accurately reflects the authors

39、opinion about rising sea levels?A. Sea levels would rise without global warming.B. Rising sea levels can be reversed.C. The results of rising sea levels will be serious.D. Sea levels are rising: because of new glaciers.（分数：1.00）A.B.C.D.(12).Look at the four squares, , , and （分数：1.00）A.B.C.D.(13).Dir

40、ections: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented, in t

41、he passage or are minor ideas in the passage. This question is worth 2 points.Global warming is causing a rise in sea levels, with accompanying changes in coastal boundaries as well as social and economic ramifications._Answer ChoicesA. The ice shelf called Larsen-A suddenly disintegrated in 1995.B.

42、 Thermal expansion due to the warming of ocean water will cause about one quarter of the rise in sea level.C. Continental ice shelves and grounded ice sheets from Antarctica to the Polar cap are melting into the oceans.D. Beginning in 1916, the Scripps Institute of Oceanography in California has doc

43、umented ocean temperatures.E. The melting of glacial ice on high mountain ranges will affect regional water resources worldwide.F. Scientists at NASA have concluded that the ice sheet in Greenland is melting at a rate of about 1 meter every year.（分数：1.00）填空项 1:_三、Passage 3(总题数：1，分数：13.00)Biological

44、Barriers and PathwaysVirtually all living things have some way of getting from here to there. Animals may walk, swim, or fly. Plants and their seeds drift on wind or water or are carried by animals. Therefore, it is reasonable to expect that, in time, all species might spread to every place on Earth

45、 where favorable conditions occur. Indeed, there are some cosmopolitan species. A good example is the housefly, found almost everywhere on Earth. However, such broad distribution is the rare exception. Just as barbed wire fences prevent cattle from leaving their pasture, biological barriers prevent

46、the dispersal of many species.What constitutes barriers depends on the species and its method of dispersal. Some are physical barriers. For land animals, bodies of water, chains of mountains, or deserts are effective. For example, the American bison spread throughout the open grasslands of North Ame

47、rica, but in the southern part of the continent there are deserts, so the bison could not spread there. For aquatic creatures, strong currents, differences in salinity, or land areas may serve as barriers.Some barriers involve competition with other species. A dandelion seed may be carried by the wi

48、nd to bare ground, and, if environmental factors are right, it may germinate. There is not much chance, however, that any individual seedling will survive. Most places that are suitable for the growth of dandelions are already occupied by other types of plants that are well adapted to the area. The

49、dandelion seedling must compete with these plants for space, water, light, and nutrients. Facing such stiff competition, the chances of survival are slim.For animals, some barriers are behavioral, The blue spotted salamander lives only on mountain slopes in the southern Appalachian Highlands. Although these creatures could survive in the river valleys, they never venture there. Birds that fly long distances often remain in very limited areas. Kirklands