2. 外语
  3. The comparatively treeless plains of North Africa have suffered a progressive drying up, both 【S1】______and man-made, but the re

The comparatively treeless plains of North Africa have suffered a progressive drying up, both 【S1】______and man-made, but the re

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问题     The comparatively treeless plains of North Africa have suffered a progressive drying up, both
【S1】______and man-made, but the region was【S2】______so rich in fertile soil that the district we now know as the Libyan Desert was, in the old days, part of the granary(粮仓)of the Roman Empire, and the centre of the Sahara【S3】______a busy trading population for a long period. That was when there were【S4】______. in plenty and the fields were the traditional "fields of the woods" -- clearings in the forest -- and therefore always tree【S5】______
    It is the trees that lift the water and send【S6】______into the air so that it may fall as dew or rain further on. Trees reduce the speed of the wind, and provide shelter and shade; the roots【S7】______minerals in the soil and these are carried to the leaves which, when they have fulfilled their function, return to the earth, giving the soil the combination of minerals that plants require.
    But through the ages Africa has been【S8】______. Successive invaders have felled the forest to provide grazing lands for their flocks and herds. With the removal of the essential tree cover, the water【S9】______was broken, the earth became feverish and sick, and in course of time was unable to support those who had broken the【S10】______of life by removing the earth’s green mantle -- the trees.

A)moisture                                             I)fed
B)cycle                                                J)exploited
C)water                                                K)social
D)rhythm                                               L)natural
E)contain                                              M)forest
F)trap                                                 N)usually
G)once                                                 O)trees
H)surrounded
【S2】
选项
答案G
解析 根据语法结构要求，该空要求填入一个副词，根据上下文意思应该选择once。
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大学英语四级

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