目前分類:托福閱讀 (46)

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   托福閱讀真題 Desert formation (6)

  Paragraph 5: There is little doubt, however, that desertification in most areas primarily from human activities rather than natural processes. The semiarid lands bordering the desert 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 period that are common phenomena along the desert margins, though, the pressure on the land is often far in excess if its diminished capacity, and desertification results.

               

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   托福閱讀真題 Desert formation (5)

  Paragraph 1: The 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 desertlike conditions into areas where they did not previously exists is called desertification. It has been estimated that an additional one-Fourth of the Earth’s land surface is threatened by this process.

 

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     托福閱讀真題 Desert formation (4)

  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 that 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.

 

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   托福閱讀真題 Desert formation (3)

  Four specific activities have been indentified as major contributors to the desertification processes overcultivation, overgazing 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 wate erosion.

 

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   托福閱讀真題 Desert formation (2)

  In 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 over the past few thousand years. The process may be accelerated in subsequent decades if global warming resulting from air pollution seriously increases.

 

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 托福閱讀真題 Desert formation (1)

  The deserts, which already occupy approximately a fourth of the Earth’s surface, have in recent decades been increasing at an alarming 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 additional one-fourth of the Earth’s land surface is threatened by this process.

 

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