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.
(of desertification )The extreme seriousness results from the vast areas of land and (of people affected)the tremendous numbers ,as well as from (of reversing or even slowing the process)the great difficulty .
大面积土地、大数目受影响的人类和（逆转或者放慢沙漠化进度的）困难造成极端沙漠化。
Which of sentences below best expression the essential information in the highlighted sentence in the passage?Incorrect choices change the meaning in important ways or leave out essential information.
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Desertification is a significant problem because it is so hard to reverse and affects large areas of land and great numbers of people.
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Slowing down the process of desertification is difficult because of population growth that has spread over large areas of land.
--错误，不是population growth，而是people affected；Slowing down the process of desertification也是原因之一
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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.
-----错误，only
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Desertification is extremely hard to reverse unless the population is reduced in the vast areas affected.
-----错误，不是unless ，而是if