托福閱讀tpo 2 Desert Formation 沙漠的形成原題解析

1、閱讀原文：The deserts, which already occupy approximately a fourth of the Earths land surface, have in recent decades been increasing at an alarming pace. The expansion of desertlike conditions into areas where they did not previously exist is called desertification. It has been estimated that an additio

2、nal one-fourth of the Earths land surface is threatened by this process.沙漠已經(jīng)占據(jù)了地球陸地面積約四分之一，而且最近幾十年正以驚人的速度擴(kuò)張。沙漠化是指類似沙漠的環(huán)境漫延到原本并非沙漠的區(qū)域。據(jù)估計，地球表面另外四分之一的地方正面臨沙漠化威脅。Desertification is accomplished primarily through the loss of stabilizing natural vegetation and the subsequent accelerated erosion of the so

3、il by wind and water. 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.沙漠化主要通過以下過程實(shí)現(xiàn)：首先自然植被不斷減少，隨后風(fēng)力和雨水加速了土壤的腐蝕。有的時候松散的土壤全部被風(fēng)刮走，留下石

4、質(zhì)化的表層；其它情況下細(xì)小的沙粒可能會被吹走，而正常沙粒大小的砂子不斷堆積，從而形成移動的沙丘或者沙脊。Even in the areas that retain a soil cover, the reduction of vegetation typically results in the loss of the soils ability to absorb substantial quantities of water. The impact of raindrops on the loose soil tends to transfer fine clay particles in

5、to the tiniest soil spaces, sealing them and producing 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 r

6、esults in the further loss of vegetation, so that a cycle of progressive surface deterioration is established.即便是在保留了土壤表層的區(qū)域，植被減少也已成為土壤大量吸取地下水的能力下降的典型因素。雨水對松散土壤的沖擊會把細(xì)小的粘土顆粒沖到土壤空隙中，封閉 了土壤并降低土地表層水的滲透率。地表對水的吸收急劇減少，大量水資源流失，因此土壤的腐蝕率也隨即增加。地表吸收水分的能力進(jìn)一步弱化使得土壤越發(fā)干 燥，導(dǎo)致植被的進(jìn)一步流失，于是便形成了土壤沙漠化的惡性循環(huán)。In some regions

7、, 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 over the past few thousand years. The process may be accelerated in subsequent decades if global warming

8、resulting from air pollution seriously increases.在一些地方，沙漠面積的擴(kuò)大很大程度上歸因于干燥的氣候條件。在過去的幾千年里，不斷增加的溫室效應(yīng)使得一些地方干旱問題愈發(fā)嚴(yán)重。倘若空氣污染帶來的溫室效應(yīng)繼續(xù)惡化，沙漠化進(jìn)程會在未來數(shù)十年內(nèi)加速實(shí)現(xiàn)。There is little doubt, however, that desertification in most areas results primarily from human activities rather than natural processes. The semiarid la

9、nds 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, the land may be able to respon

10、d 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.然而，可以肯定的是，大部分地區(qū)沙漠化主要都是由于人類活動造成，而非自然條件導(dǎo)致。沙漠邊緣的半干旱土地所處的生態(tài)平衡環(huán)境非常脆弱，環(huán)境壓力持續(xù)增 加，而這些半干旱區(qū)域適應(yīng)環(huán)境壓力的能力極

11、其有限。人口數(shù)量的增加使得人們不斷向土地施壓，依其提供食物和燃料。在濕潤的季節(jié)里，土地興許能夠應(yīng)付這些壓 力。但是在干旱的季節(jié)里，在沙漠周邊的土地上，存在著這樣一個十分普遍的現(xiàn)象：人類對土地施加的壓力遠(yuǎn)遠(yuǎn)超過了土地自身減壓的能力，因此最終形成了沙漠。Four specific activities have been identified as major contributors to the desertification processes: overcultivation, overgrazing, firewood gathering, and overirrigation. The

12、 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 crop failures are common. Since the raising of most crops necessitates the prior removal of the natural vegetation, c

13、rop failures leave extensive tracts of land devoid of a plant cover and susceptible to wind and water erosion.導(dǎo)致沙漠化的主要因素有四個：過度種植，過度放牧，過分砍伐，過度灌溉。由于人口密度增加，人們對糧食作物的種植已經(jīng)擴(kuò)展到日益干燥的區(qū)域進(jìn)行。這些區(qū)域 很有可能經(jīng)常會發(fā)生干旱，所以農(nóng)作物種植失敗是很正常的事情。大多數(shù)農(nóng)作物的種植需要事先移除天然植被，而農(nóng)作物欠收后又會留下大面積荒地，非常容易被風(fēng) 力和雨水侵蝕。The raising of livestock is a major e

14、conomic 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 pulverization of the soil. This is usually followed by the

15、drying of the soil and accelerated erosion.在半干旱地區(qū)，草坪是主要的天然植被，家畜飼養(yǎng)是當(dāng)?shù)氐囊豁椫饕?jīng)濟(jì)活動。在一個地區(qū)過量飼養(yǎng)家畜會導(dǎo)致植被覆蓋面積減少，土地被大量踐踏和碾碎。通常，隨之而來的就是土地硬化和加速侵蝕。Firewood 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 t

16、hat many cities 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.在很多國家木材是用來

17、做飯和加熱的最主要燃料。人口增加帶來的壓力促使人們大量砍伐木材，導(dǎo)致許多城市和鄉(xiāng)村周圍大面積樹木和灌木減少。同時人們大量使用烘干的動物排泄物作為替代燃料同樣對土壤不利，因為這些珍貴的土壤成分調(diào)節(jié)劑和植物營養(yǎng)資源將不會再回歸至土壤當(dāng)中。The 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

18、exists, the water table rises, bringing dissolved salts to the surface. The water evaporates and the salts are left behind, creating a white crustal layer that prevents air and water from reaching the underlying soil.造成土地沙漠化的最后一個主要人為因素在于人類過度灌溉導(dǎo)致土壤的鹽堿化。灌溉多余的水滲透到地下水位。假如沒有排水系統(tǒng)的存在，那么地下水位上升，把溶解的鹽分帶到土壤表面。

19、水分蒸發(fā)后，鹽分留在了表面，形成白色的地殼層，這一地殼層阻止了空氣和水接觸地底下的土壤。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. Once the soil has been removed by erosion, only the

20、 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 to reverse the present deterioration of the surface.沙漠化問題異常嚴(yán)重，這是因為有佷廣闊的地區(qū)和數(shù)量龐大的人群都受到了

21、沙漠化的影響，而且要想逆轉(zhuǎn)沙漠化的進(jìn)程甚至減緩沙漠化的速度都面臨著巨大的困難。 一旦土壤被侵蝕，需要再經(jīng)過幾百到上千年的時間才會產(chǎn)生新的土壤。那些大量土壤仍保存完好的地方，亟需一個嚴(yán)謹(jǐn)而有力的保護(hù)政策和植被覆蓋計劃來保護(hù)現(xiàn)有 土地。第1題：The word threatened in the passage is closest in meaning toA：RestrictedB：EndangeredC：PreventedD：Rejected解析：threatened 受到威脅的，很容易選出B選項，endangered, 使危險。依據(jù)上下文，前句說什么是desertification, 本句

22、說還有14的土地被這種過程（沙漠化）如何，也很容易猜出選項。第2題：According to paragraph 3, the loss of natural vegetation has which of the following consequences for soil?A：Increased stony contentB：Reduced water absorptionC：Increased numbers of spaces in the soilD：Reduced water runoff解析：This is a Factual Information question aski

23、ng for specific information that can be found in paragraph 3. Thecorrect answer is choice 2, reduced water absorption. The paragraph explicitly states that the reduction ofvegetation greatly reduces water absorption. Choice 4, reduced water runoff, explicitly contradicts theparagraph, so it is incor

24、rect. The spaces in the soil are mentioned in another context: the paragraph doesnot say that they increase, so choice 3 is incorrect. The paragraph does not mention choice第3題：The word delicate in the passage is closest in meaning toA：FragileB：PredictableC：ComplexD：Valuable解析：This is a Vocabulary qu

25、estion. The word being tested is delicate. It is highlighted in the passage. The correctanswer is choice 1, fragile, meaning easily broken. Delicate has the same meaning as fragile.第4題：According to paragraph 5, in dry periods, border areas have difficultyA：Adjusting to stresses created by settlement

26、B：Retaining their fertility after desertificationC：Providing water for irrigating cropsD：Attracting populations in search of food and fuel解析：根據(jù)dry period 定位本段末句，說在沙漠邊緣典型的干旱期，對土地的壓力經(jīng)常遠(yuǎn)遠(yuǎn)超過土讀弱化的能力，從而導(dǎo)致沙漠化。并且前句說，在濕潤季節(jié)，土地或許能回應(yīng)這些壓力。前后對比可知干旱期不能回應(yīng)這些壓力。A 正確，本句和前句內(nèi)容概括。B錯，沙漠化之后的結(jié)果沒有提到。C錯，沒有提到。D錯，沒有提到。第5題：The w

27、ord progressively in the passage is closest in meaning toA：OpenlyB：ImpressivelyC：ObjectivelyD：Increasingly解析：progressively, 由詞跟gress走和前綴pro向前可知詞義大致是進(jìn)步的，前進(jìn)的，增加的。D正確。A公開的，B印象深刻的，C客觀的都不對。第6題：According to paragraph 6, which of the following is often associated with raising crops?A：Lack of proper irrigat

28、ion techniquesB：Failure to plant crops suited to the particular areaC：Removal of the original vegetationD：Excessive use of dried animal waste解析：This is a Factual Information question asking for specific information that can be found in paragraph 6. Thecorrect answer is choice 3, removal of the origi

29、nal vegetation. Sentence 4 of this paragraph says that theraising of most crops necessitates the prior removal of the natural vegetation, an explicit statement ofanswer choice 3. Choice 1, lack of proper irrigation techniques, is incorrect because the paragraph mentionsoverirrigation as a cause of d

30、esertification. No irrigation techniques are discussed. Choices 2 and 4,failure to plant suitable crops and use of animal waste, are not discussed.第7題：The phrase devoid of in the passage is closest in meaning toA：Consisting ofB：Hidden byC：Except forD：Lacking in解析：devoid of 缺乏，很容易選出D。根據(jù)上下文，本句后段說，and

31、susceptible to wind and water erosion. 該段讀懂也能猜出詞義。A 組成，B隱藏，C除外都不對。第8題：According to paragraph 9, the grounds absorption of excess water is a factor in desertification because it canA：Interfere with the irrigation of landB：Limit the evaporation of waterC：Require more absorption of air by the soilD：Bri

32、ng salts to the surface解析：根據(jù)absorption of excess water定位，找到excess water from irrigation sinks into the water table. 后句提到，bringing dissolved salts to the surface. 可知D正確。A 錯，沒有提到。B錯，沒有提到。C錯，沒有提到。第9題：All of the following are mentioned in the passage as contributing to desertification EXCEPTA：Soil erosi

33、onB：Global warmingC：Insufficient irrigationD：The raising of livestock解析：This is a Negative Factual Information question asking for specific information that can be found in thepassage. Choice 3, insufficient irrigation, is the correct answer. Choice 1, soil erosion, is explicitlymentioned in paragra

34、ph 2 as one of the primary causes of desertification, so it is not the correct answer.Choice 2, global warning, is mentioned as a cause of desertification in paragraph 4, so it is incorrect. Choice4, raising of livestock, is described in paragraph 7 as another cause of desertification, so it is inco

35、rrect. Thepassage includes excessive irrigation as a cause of desertification, but not its opposite, insufficient irrigation,so that is the correct answer. 第10題：Which of the sentences below best expresses the essential information in the highlighted sentence in the passage?Incorrect choices change t

36、he meaning in important ways or leave out essential information.A：Desertification is a significant problem because it is so hard to reverse and affects large areas of land and great numbers of people.B：Slowing down the process of desertification is difficult because of population growth that has spr

37、ead over large areas of land.C：The spread of deserts is considered a very serious problem that can be solved only if large numbers of people in various countries are involved in the effort.D：Desertification is extremely hard to reverse unless the population is reduced in the vast areas affected.解析：原

38、句含有一個弱因果關(guān)系results from. 沙漠化的嚴(yán)重性來自3個方面：受影響土地面積大，受影響人口多，恢復(fù)困難。A正確，只改變了原句敘述順序。B錯，改變了因果關(guān)系。C錯，增加了條件關(guān)系。D錯，增加了條件關(guān)系。第11題：It can be inferred from the passage that the author most likely believes which of the following about the future of desertification?A：Governments will act quickly to control further desert

39、ification.B：The factors influencing desertification occur in cycles and will change in the future.C：Desertification will continue to increase.D：Desertification will soon occur in all areas of the world解析：推理題，由整篇文章，尤其是末段可以推斷出作者對于沙漠化持悲觀態(tài)度，C與此態(tài)度一致。A不能推出，末段末句說，嚴(yán)格的政策可能may 改變沙漠化進(jìn)程，但沒有A確定推斷。B錯，3段提到有可能惡性循環(huán)，

40、但不能確定改變。D錯，該選項過于悲觀。文章首段提到additional one-fourth of the Earths land surface, 但沒有說全部地區(qū)第12題：Look at the four squares that indicate where the following sentence can be added to the passage. Where would the sentence best fit?This economic reliance on livestock in certain regions makes large tracts of land susceptible to overgrazing. 解析：插入句說，特定地區(qū)對于牲畜的經(jīng)濟(jì)依賴導(dǎo)致大片土地易于被過度放牧。由B位置后句consequence推斷，正好和插入句構(gòu)成因果關(guān)系。第13題：Directions: An introductory sentence for a brief summary