托福閱讀OGDesertFormation答案與解析

1、Desert Formation1 .核心詞匯總結(jié)occupy占據(jù)approximately 大約previously 以前desertification 沙漠化estimate 估計vegetation 植被typically作為特色地substantial 大量的impact影響,效果，撞擊particle 顆粒seal密封penetration 滲透absorption 吸收consequently 因此，結(jié)果erosion 侵蝕diminish 減弱deterioration 惡化primarily主要地semiarid半干旱的delicate脆弱的devoid缺乏的salinizat

2、ion 鹽堿化evaporation 蒸發(fā)millennia 千年rigorously 嚴(yán)格地2 .長難句總結(jié)(1) The extreme seriousness of desertification results from the vast areas of land and the tremendous numbers of people affected, as well as from the great difficulty of reversing or even slowing the process.(2) Even in the areas that retain a s

3、oil cover, the reduction of vegetation typically results in the loss of the soil's ability to absorb substantial quantities of water.(3) The semiarid lands bordering the deserts exist in a delicate ecological balance and are limited in their potential to adjust to increased environmental pressur

4、es.(4) During the dry periods that are common phenomena along the desert margins, though, the pressure on the land is often far in excess of its diminished capacity, and desertification results.(5) The consequences of an excessive number of livestock grazing in an area are the reduction of the veget

5、ation cover and the trampling and pulverization of the soil.Pl： introductionThe deserts, which already occupy approximately a fourth of the Earth's land surface, have in recent decades been increasing at an alarming pace. The expansion of desert-like conditions into areas where they did not prev

6、iously exist is called desertification. It has been estimated that an additional one-fourth of the Earth's land surface is threatened by this process.P2： Cause-1 erosion-windDesertification is accomplished primarily through the loss of stabilizing natural vegetation and the subsequent accelerate

7、d erosion of the soil by wind and water (9-A). In some cases the loose soil is blown completely away, leaving a stony surface. In other cases, the finer particles may be removed, while the sand-sized particles are accumulated to form mobile hills or ridges of sand.P3: Cause-1 erosion-waterEven in th

8、e areas that retain a soil cover, the reduction of vegetation typically results in the loss of the soil's ability to absorb substantial quantities of water (2). The impact of raindrops on the loose soil tends to transfer fine clay particles into the tiniest soil spaces, sealing them and producin

9、g a surface that allows very little water penetration. Water absorption is greatly reduced; consequently runoff is increased, resulting in accelerated erosion rates. The gradual drying of the soil caused by its diminished ability to absorb water results in the further loss of vegetation, so that a c

10、ycle of progressive surface deterioration is established.P4： Cause-2 climate-global warmingIn some regions, the increase in desert areas is occurring largely as the result of a trend toward drier climatic conditions. Continued gradual global warming has produced an increase in aridity for some areas

11、 over the past few thousand years (9-B), The process may be accelerated in subsequent decades if global warming resulting from air pollution seriously increases.P5： Cause-3 peopleThere is little doubt, however, that desertification in most areas results primarily from human activities rather than na

12、tural processes. The semiarid lands bordering the deserts exist in a delicate ecological balance and are limited in their potential to adjust to increased environmental pressures. Expanding populations are subjecting the land to increasing pressures to provide them with food and fuel. In wet periods

13、, the land may be able to respond to these stresses. During the dry periods that are common phenomena along the desert margins, though, the pressure on the land is often far in excess of its diminished capacity and desertification results (4).P6： Cause-3 people- overcultivationFour specific activiti

14、es have been identified as major contributors to the desertification processes: overcultivation, overgrazing, firewood gathering, and overirrigation. The cultivation of crops has expanded into progressively drier regions as population densities have grown. These regions are especially likely to have

15、 periods of severe dryness, so that crop failures are common. Since the raising of most crops necessitates the prior removal of the natural vegetation, crop failures leave extensive tracts of land devoid of a plart cover and susceptible to wind and water erosion .P7： Cause-3 people- overgrazingThe r

16、aising of livestock is a major economic activity in semiarid lands, where grasses are generally the dominant type of natural vegetation. The consequences of an excessive number of livestock grazing in an area are the reduction of the vegetation cover and the trampling and pukerization of the soil（9-

17、D）. This is usually followed by the drying of the soil and accelerated erosion.P8： Cause-3 people- firewood gatheringFirewood is the chief fuel used for cooking and heating in many countries. The increased pressures of expanding populations have led to the removal of woody plants so that many cities

18、 and towns are surrounded by large areas completely lacking in trees and shrubs. The increasing use of dried animal waste as a substitute fuel has also hurt the soil because this valuable soil conditioner and source of plant nutrients is no longer being returned to the land.P9： Cause-3 people- overi

19、rrigationThe final major human cause of desertification is soil salinization resulting from overirrigation. Excess water from irrigation sinks down into the water table. If no drainage system exists, the water table rises, bringing dissolved salts to the surface （8）, The water evaporates and the sal

20、ts are left behind, creating a white crustal layer that prevents air and water from reaching the underlying soil.PIO： conclusionThe extreme seriousness of desertification results from the vast areas of land and the tremendous numbers of people affected, as well as from the great difficulty of revers

21、ing or even slowing the process. Once the soil has been removed by erosion, only the passage of centuries or millennia will enable new soil to form. In areas where considerable soil still remains, though, a rigorously enforced program of land protection and cover-crop planting may make it possible t

22、o reverse the present deterioration of the surface.Paragraph 1: The deserts, which already occupy（占據(jù)）approximately（大約）a fourth of the Earth's land surface, have in recent decades been increasing at an alarming pace（以驚人的速度）.The expansion of desert-like conditions into areas where they did not pre

23、viously 以前）exist is called desertification（沙漠化）. It has been estimated（估計）that an additional one-fourth of the Earth's land surface is threatened by this process.1. The word “threatened 威脅"in the passage is closest in meaning to 詞匯題 o restricted 限制o endangered danger 危險 enlargeo prevented 阻

24、止 o rejected 拒絕Paragraph 3: Even in the areas that retain a soil cover, the reduction of vegetation（植 被）typically（作為特色地）results in the loss of the soil's ability to absorb substantial（大戰(zhàn)的）quantities of water. The impact（影響，效果）of raindrops on the loose soil tends to transfer fine clay particles（顆

25、米立）into the tiniest soil spaces, sealing（密封）them and producing a surface that allows very little water penetration（滲透）.Water absorption（吸收）is greatly reduced; consequently（因此， 結(jié)果）runoff is increased, resulting in accelerated erosion（侵蝕）rates. The gradual drying of the soil caused by its diminished（減

26、弱的）ability to absorb water results in the further loss of vegetation, so that a cycle of progressive surface deterioration（惡 化）is established.2. According to paragraph 3, the loss of natural vegetation has which of the following consequences for soil?細(xì)節(jié)題o Increased stony content o Reduced water abso

27、rption o Increased numbers of spaces in the soil o Reduced water runoffParagraph 5: There is little doubt, however, that desertification in most areas results primaily（主要地）from human activities rather than natural processes. The semiarid（半干旱 的）lands bordering the deserts exist in a delicate （脆弱的） ec

28、ological balance and are limited in their potential to adjust to increased environmental pressures. Expanding populations are subjecting the land to increasing pressures to provide them with food and fuel. In wet periods, the land may be able to respond to these stresses. During the dry periods that

29、 are common phenomena along the desert margins, though, the pressure on the land is often far in excess of （超過）its diminished capacity, and desertification results.3. The word "delicate" in the passage is closest in meaning to 詞匯題 o fragileo predictable o complex o valuable4. According to

30、paragraphborder areas have difficulty 細(xì)節(jié)題 o adjusting to stresses created by settlement o retaining their fertility after desertification o providing water for irrigating cropso attracting populations in search of food and fuelParagraph 6: Four specific activities have been identified as major contr

31、ibutors to the desertification processes: overcultivation, overgrazing, firewood gathering, and overirrigation. The cultivation of crops has expanded into progressively drier regions as population densities have grown. These regions are especially likely to have periods of severe dryness, so that cr

32、op failures are common. Since the raising of most crops necessitates the prior removal of the natural vegetation, crop failures leave extensive tracts of land devoid（缺乏的）of a plant cover and susceptible（易受 影響的）to wind and water erosion.5. The word “progressively" in the passage is closest in me

33、aning to 詞¥題 o openlyo impressively o objectively o increasingly6. According to paragraph 6, which of the following is often associated with raising crops?細(xì)節(jié)題o Lack of proper irrigation techniqueso Failure to plant crops suited to the particular area o Removal of the original vegetation o Exces

34、sive use of dried animal waste7. The phrase “devoid of“ in the passage is closest in meaning to 詞匯題 o consisting of o hidden by o except for o lacking inParagraph 9: The final major human cause of desertification is soil salinization（鹽利成 化）resulting from overirrigation. Excess water from irrigation

35、sinks down into the water table. If no drainage system exists, the water table rises, bringing dissolved salts to the surface. The water evaporates （蒸發(fā)）and the salts are left behind, creating a white crustal layer that prevents air and water from reaching the underlying soil.8. According to paragrap

36、h 9, the ground's absorption of excess water is a factor in desertification because it can 細(xì)節(jié)題o interfere with the irrigation of land o limit the evaporation of water o require more absorption of air by the soilo bring salts to the surface9. All of the following are mentioned in the passage as c

37、ontributing to desertification EXCEPT 選非題o soil erosiono global warming o insufficient irrigation o the raising of livestockParagraph 10: The extreme seriousness of desertification results from the vast areas of land and the tremendous numbers of people affected, as well as from the great difficulty

38、 of reversing or even slowing the process. Once the soil has been removed by erosion, only the passage of centuries or m川ennia（千年）will enable new soil to form. In areas where considerable soil still remains, though, a rigorously儼格地） enforced program of land protection and cover-crop planting may mak

39、e it possible to reverse the present deterioration of the surface.10. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage? Incorrect choices change the meaning in important ways or leave out essential information. 句子簡化題o Desertification is

40、 a significant problem because it is so hard to reverse and affects large areas of land and great numbers of people.o Slowing down the process of desertification is difficult because of population growth that has spread over large areas of land.o The spread of deserts is considered a very serious pr

41、oblem that can be solved only if large numbers of people in various countries are involved in the effort.o Desertification is extremely hard to reverse unless the population is reduced in the vast areas affected.11. It can be inferred from the passage that the author most likely believes which of th

42、e following about the future of desertification? 推斷題o Governments will act quickly to control further desertification.o The factors influencing desertification occur in cycles and will change in the future, o Desertification will continue to increase.o Desertification will soon occur in all areas of

43、 the world.Paragraph 7: 0The raising of livestock is a major economic activity in semiarid lands, where grasses are generally the dominant type of natural vegetation.回The consequences of an excessive number of livestock grazing in an area are the reduction of the vegetation cover and the trampling and pulverization of the soil. 酊his is usually followed by the drying of the soil and accelerated erosion.團(tuán)12. Look at the four squares E that