根据短文内容,从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。           Cau...

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根据短文内容, 从短文后的选项中选出能填入空白处的最佳选项。选项中有两项为多余选项。           

Causes of sandstorms

In desert areas, dust sandstorms are most common caused by either thunderstorm outflows, or by strong pressure gradients (气压梯度) which cause an increase in wind speed over a wide area. In some cases, dust and sand may set a limit to a shallow depth by a low-lying temperature change,      1      

Drought is another cause of sandstorms, Poor farming practices make dust and sand free of protection from the wind.      2      A sandstorm can transport and carry large amounts of sand. Desert is a key source of sandstorms. Saharan sandstorms have increased about 10 times during the half century since the 1950s, causing topsoil loss in nearby countries. In Mauritania there were just two sandstorms a year in the early 1960s, but there are 80 a year today.

    3      

Sandstorms have also been shown to increase the spread of diseases across the globe. The virus In the dust is blown into the atmosphere by the storms. Some diseases may not be urgent at the very beginning, but they can develop into deadly ones if left untreated.     4     

Sandstorms cause soil loss from the dry lands, doing harm to agriculture. Sandstorms also reduce visibility (能见度) affecting airplanes and road transportation,     5      

Dust can also have good effects. Central and South American rainforests get most of their mineral nutrients from the Sahara; iron-poor ocean regions get iron.

A. Effects of sandstorms.

B. Bad results caused by sandstorms.

C. People know little about the effects of sandstorms.

D. In other cases, dust may be lifted as high as 6, 100 meters high.

E. Dryland farming is one of the most serious practices.

F. For example, a breathing problem can lead to lung cancer, while dry eyes

G. In addition, sandstorms also discourage visitors from visiting these places, which will strike tourism

【回答】

 D  E  A  F   G

知识点：七选五题型

题型：阅读理解