17、She (longed) to be envied and sought after.

A.hoped
B.wished
C.was eager
D.wanted

18、The teachers want to (do away with) cheating in their school.

A.put an end to
B.retain
C.do credit to
D.substitute for

19、The mail was (delayed) for two days because of the snow storm.

A.held in
B.held up
C.held down
D.held off

20、He is always (under the weather).

A.travelling
B.sick
C.away
D.Unconscious

21、第一篇 Soil Erosion responsible for maintaining soil fertility and moisture. Why is it that under certain circumstances, the plant cover is unable to r egenerate itself, thus setting the stage for serious erosion? To answer this que stion, let us take an extreme example, the destruction of tropical rain forests. In general, the equatorial soil is poor: forests can exist in these regions onl y because they are part of a balanced cycle. All that the forest produces is ret urned to the forest. The organic matter that falls from the trees constitutes th e humus that the forest requires. When man cuts down all the trees to make room for crops, the soil is laid bare and, deprived of shade, heats up. An increase I n soil temperature increases that rate of d***mposition of organic matter. Organ ic nitrogen is converted into soluble ammonia and nitrates, which the rains quic kly leach away. It has been calculated that a rise in temperature from 77℃ to 7 8.8℃ may increase the loss of nitrogen by fifteen to twenty pounds per acre per y ear. With the fertility of the soil destroyed, an irreversible change from fores t to desert can be initiated.It was once thought that changes of climate adversely affected North Africa. Geologists have now____this.

A.confirmed
B.disproved
C.favoured
D.supported

22、(同21题)The “evidence" mentioned in line 3 evidently refers to

A.factors not mentioned in the passage.
B.the soil.
C.climatic conditions and their influence on the land.
D.the nature of the earth.

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