问题 选择题

下列加速土地沙漠化进程的人为原因有(  )

A.滥垦林草,过度放牧,滥挖发菜、甘草

B.草原发展种植业,降水稀少,水资源不足

C.退耕还草,退耕还林,涵养水源

D.沙尘暴肆虐,水土流失严重,退田还湖

答案

人为原因:过度放牧、粗放经营、盲目垦荒、水资源的不合理利用、过度砍伐森林、不合理开矿等是人类活动加速荒漠化扩展的主要表现.乱挖中药材、毁林等更是直接形成土地荒漠化的人为活动.另外,不合理灌溉方式也造成了耕地次生盐渍化.

自然原因有;降水稀少,气候干旱;.大风日多且集中;.土质疏松;近年来频繁发生于我国西北、华北(北部)地区的沙尘暴,更加剧了荒漠化过程.

故选:A.

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     Nobody has ever succeeded in their attempt to stay young and live a very long life. 1_____ But is this

really true?

     Dr Aubrey de Grey thinks that we can stop people getting old and that in about 20 years, people will

be able to live to be 1,000 years old! 2_____    

     In Dr Grey's opinion, getting old is a problem that can be solved. 3_____ If we can cure this disease,

we can stop the aging process. We can also make people have young bodies again.

     Dr Grey believes that science will soon be able to stop the causes of aging so that a person's body

won't get weak and won't suffer from the typical diseases of old age.

     Dr Grey compares the human body to a house. As the house gets older, some things must be repaired.

Broken hearts must be replaced. The same thing can happen with the human body, he thinks. We can use

stem cell technology to grow new, healthy tissue to replace the old, damaged one. We can also try to remove

disease-causing molecules in our bodies. 4_____. 

     5_____ However, they admit that Dr Grey's ideas have not yet been proved wrong. Dr Grey is convinced

that his opinions are realistic and that his research is very important. If aging is a disease, he says, we must

try to cure it.

A. At the same time, people's bodies will stay young and healthy.

B. Scientists succeed in solving the problem of aging long ago.

C. A lot of scientists think his ideas not realistic.

D. When our bodies change as we get older, this is like a disease.

E. New deadly diseases may also be cured, if we can stop the aging process.

F. It seems that everybody must get old and die.

G. In this way, a person could easily live to be 1,000 years old.