托福阅读：TPO2(Desert Formation)原文及答案

　　1. The word threatened in the passage is closest in meaning to

　　Restricted

　　Endangered

　　Prevented

　　Rejected

　　Paragraph 3: Even in the 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. The impact of raindrops on the loose soil tends to transfer fine clay particles into 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 results in the further loss of vegetation, so that a cycle of progressive surface deterioration is established.

　　2. According to paragraph 3, the loss of natural vegetation has which of the following consequences for soil?

　　Increased stony content

　　Reduced water absorption

　　Increased numbers of spaces in the soil

　　Reduced water runoff

　　Paragraph 5: There is little doubt, however, that desertification in most areas results primarily from human activities rather than natural 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, 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.

　　3. The word delicate in the passage is closest in meaning to

　　Fragile

　　Predictable

　　Complex

　　Valuable

　　4. According to paragraph 5, in dry periods, border areas have difficulty

　　Adjusting to stresses created by settlement

　　Retaining their fertility after desertification

　　Providing water for irrigating crops

　　Attracting populations in search of food and fuel

　　Paragraph 6: Four specific activities 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 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 plant cover and susceptible to wind and water erosion.

　　5. The word progressively in the passage is closest in meaning to

　　Openly

　　Impressively

　　Objectively

　　Increasingly

　　6. According to paragraph 6, which of the following is often associated with raising crops?

　　Lack of proper irrigation techniques

　　Failure to plant crops suited to the particular area

　　Removal of the original vegetation

　　Excessive use of dried animal waste