Paragraph 7:■ The raising 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 pulverization of the soil. ■This is usually followed by the drying of the soil and accelerated erosion.■

12. Look at the four squares [■] that indicate where the following sentence can be added to the passage.
This economic reliance on livestock in certain regions makes large tracts of land susceptible to overgrazing.
Where would the sentence best fit?

13-14. Directions: 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 answer choices 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.

Many factors have contributed to the great increase in desertification in recent decades.
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Answer Choices
1. Growing human populations and the agricultural demands that come with such growth have upset the ecological balance in some areas and led to the spread of deserts.
2. As periods of severe dryness have become more common, failures of a number of different crops have increased.
3. Excessive numbers of cattle and the need for firewood for fuel have reduced grasses and trees, leaving the land unprotected and vulnerable.
4. Extensive irrigation with poor drainage brings salt to the surface of the soil, a process that reduces water and air absorption.
5. Animal dung enriches the soil by providing nutrients for plant growth.
6. Grasses are generally the dominant type of natural vegetation in semiarid lands.

 
參考答案：
1. ○2
This is a Vocabulary question. The word being tested is threatened. It is highlighted in the passage. To threaten means to speak or act as if you will cause harm to someone or something. The object of the threat is in danger of being hurt, so the correct answer is choice 2, "endangered."

2. ○2
This is a Factual Information question asking for specific information that can be found in paragraph 3. The correct answer is choice 2, reduced water absorption. The paragraph explicitly states that the reduction of vegetation greatly reduces water absorption. Choice 4, reduced water runoff, explicitly contradicts the paragraph, so it is incorrect. The "spaces in the soil" are mentioned in another context: the paragraph does not say that they increase, so choice 3 is incorrect. The paragraph does not mention choice 1.

3. ○1
This is a Vocabulary question. The word being tested is delicate. It is highlighted in the passage. The correct answer is choice 1, "fragile," meaning "easily broken." Delicate has the same meaning as "fragile."

4. ○1
This is a Factual Information question asking for specific information that can be found in paragraph 5. The correct answer is choice 1: border areas have difficulty "adjusting to stresses created by settlement." The paragraph says that "expanding populations," or settlement, subject border areas to "pressures," or stress, that the land may not "be able to respond to." Choice 2 is incorrect because the paragraph does not discuss "fertility" after desertification. Choice 3 is also incorrect because "irrigation" is not mentioned here. The paragraph mentions "increasing populations" but not the difficulty of "attracting populations," so choice 4 is incorrect.

5. ○4
This is a Vocabulary question. The word being tested is progressively. It is highlighted in the passage. The correct answer is choice 4, "increasingly." Progressively as it is used here means "more," and "more" of something means that it is increasing.

6. ○3
This is a Factual Information question asking for specific information that can be found in paragraph 6. The correct answer is choice 3, "removal of the original vegetation." Sentence 4 of this paragraph says that "the raising of most crops necessitates the prior removal of the natural vegetation," an explicit statement of answer choice 3. Choice 1, lack of proper irrigation techniques, is incorrect because the paragraph mentions only "overirrigation" as a cause of desertification. No irrigation "techniques" are discussed. Choices 2 and 4, failure to plant suitable crops and use of animal waste, are not discussed.

7. ○4
his is a Vocabulary question. A phrase is being tested here, and all of the answer choices are phrases. The phrase is "devoid of." It is highlighted in the passage. "Devoid of' means "without," so the correct answer is choice 4, "lacking in." If you lack something that means you are without that thing.

8. ○4
This is a Factual Information question asking for specific information that can be found in paragraph 9. The correct answer is choice 4, "bring salts to the surface." The paragraph says that the final human cause of desertification is salinization resulting from overirrigation. The paragraph goes on to say that the overirrigation causes the water table to rise, bringing salts to the surface. There is no mention of the process "interfering" with or "limiting" irrigation, or of the "amount of air" the soil is required to absorb, so choices 1,2, and 3 are all incorrect.

9. ○3
This is a Negative Factual Information question asking for specific information that can be found in the passage. Choice 3, "insufficient irrigation," is the correct answer. Choice 1, "soil erosion," is explicitly mentioned in paragraph 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. Choice 4, "raising of livestock," is described in paragraph 7 as another cause of desertification, so it is incorrect. The passage includes excessive irrigation as a cause of desertification, but not its opposite, insufficient irrigation, so that is the correct answer.

10. ○1
This is a Sentence Simplification question. As with all of these items, a single sentence in the passage is highlighted:

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.

The correct answer is choice 1. That choice contains all of the essential information in the highlighted sentence and does not change its meaning. The only substantive difference between choice 1 and the tested sentence is the order in which he information is presented. Two clauses in the highlighted sentence, "The great difficulty of reversing the process" and "the numbers of people affected," have simply been reversed; no meaning has been changed, and no information has been removed. Choices 2,3, and 4 are all incorrect because they change the meaning of the highlighted sentence.

11. ○3
This is an Inference question asking for an inference that can be supported by the passage. The correct answer is choice 3; the passage suggests that the author believes "Desertification will continue to increase." The last paragraph of the passage says that slowing or reversing the erosion process will be very difficult, but that it may occur in those areas that are not too affected already if rigorously enforced anti-erosion processes are implemented. Taken together, this suggests that the author is not confident this until happen; therefore, it can be inferred that he thinks erosion will continue. The passage provides no basis for inferring choices 1, 2, or 4.

12. ○2
This is an Insert Text question. You can see the four black squares in paragraph
7 that represent the possible answer choices here:

■The raising of live stock 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 pulverization of the soil. ■This is usually followed by the drying of the soil and accelerated erosion. ■
 The sentence provided, "This economic reliance on livestock in certain regions makes large tracts of land susceptible to overgrazing," is best inserted at Square 2. The inserted sentence refers explicitly to relying on "livestock in certain regions." Those regions are the ones described in the sentence preceding square2, which states that raising livestock is "a major economic activity in semiarid lands." The inserted sentence then explains that this reliance "makes large tracts of land susceptible to overgrazing. " The sentence that follows square 2 goes on to say that "The consequences of an excessive number of livestock grazing in an area are. . ." Thus, the inserted sentence contains references to both the sentence before square 2 and the sentence after square 2. This is not true of any of the other possible insert points, so square 2 is correct.

13-14.○1 3 4
This is a Prose Summary question. It is completed correctly below. The correct choices are 1, 3, and 4. Choices 2, 5, and 6 are therefore incorrect.

 
參考譯文：
沙漠已經(jīng)占據(jù)了地球表面積約四分之一，而且最近幾十年正以驚人的速度擴張。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。

沙漠化主要通過以下過程實現(xiàn)：首先自然植被不斷減少，隨后風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刮走，留下石質(zhì)化的表層；其它情況下細小的沙�？赡軙�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。

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一步弱化使得土壤越發(fā)干燥，導致植被的進一步流失，于是便形成了土壤沙漠化的惡性循環(huán)。

在一些地方，沙漠面積的擴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使得一些地方干旱問題愈發(fā)嚴重。倘若空氣污染帶來的溫室效應繼續(xù)惡化，沙漠化進程會在未來數(shù)十年內(nèi)加速實現(xiàn)。

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)域適應環(huán)境壓力的能力極其有限。人口數(shù)量的增加使得人們不斷向土地施壓，依其提供實物和燃料。在濕潤的季節(jié)里，土地興許能夠應付這些壓力。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遠超過了土地自身減壓的能力，因此最終形成了沙漠。

導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)擴展到日益干燥的區(qū)域進行。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。種植大量農(nóng)作物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，非常容易被風力和雨水侵蝕。

在半干旱地區(qū)，草坪是主要的天然植被，家畜飼養(yǎng)是當?shù)氐囊豁椫饕��?jīng)濟活動。在一個地區(qū)過量飼養(yǎng)家畜會導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。

在很多國家木材是用來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中。

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。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。

沙漠化問題異常嚴重，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沙漠化的影響，而且要想逆轉沙漠化的進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，亟需一個嚴謹而有力的保護政策和植被覆蓋計劃來保護現(xiàn)有土地。