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　　第二篇 Deforestation and Desertification(沙漠化)

　　TheSahel zone lies between the Saharadesert and the fertile savannahs(熱帶大草原)ofnorthern Nigeria and South Sudan. The word sahel comes from Arabic and means marginal or transitional ,andthis is a good description of thesesemi-arid(半干旱)lands,whichoccupy much of the Western African countries of Mail,Mauritania,Niger,and Chad.

　　Unfortunately, over the last century theSahara desert has steadily crept southwards eating into once productive Sahellands. United Nations surveys show that over 70 percent of the dry land inagriculture use in Africa has deterioratedover the last 30 years. Droughts have become more severe, the most recentlasting over twenty years in parts of the Sahel region. The same process ofdesertification is taking place across southern Africa as the Kalahari desertadvances into Botswana and parts of South Africa.

　　One ofthe major causes of this desert advance ispoor agricultural land use, driven by the pressures of increasing population.Overgrazing一 keeping too many farm animals on the land一means that grasses and other plants cannot recover, and scarce water suppliesare exhausted. Overcultivation一 tryingto grow too many crops on poor land一 resultsin the soil becoming even less fertile and drier, and beginning to break up. Soilerosion (侵蝕) follows, and the land turns into desert.

　　Another cause of desertification is loss of tree cover. Trees are cutdown for use as fuel and to clear land for agricultural use. Tree roots help tobind the soil together, to conserve moisture, and to provide a habitat forother plants and animals. When trees are cut down, the soil begins to dry andloosen, wind and rain erosion increase, other plant species die, and eventuallythe fertile top soil may be almost entirely lost, leaving only bare rock anddust.

　　The effects of loss of topsoil and increased drought are irreversible. Theyare,however, preventable. Careful conservation of tree cover and sustainableagricultural land use have been shown to halt deterioration of soils and lessenthe effects of shortage of rainfall. One project in Kita in south-west Malifunded by UNDP has involved local communities in sustainable management offorest,while at the same time providing a viable(有活力的)agriculturaleconomy. This may be a model for similar projects in otherWest African countries.

　　35 order to prevent desertification,the author proposes ___.

　　A. making good use of international aids

　　B. developing a sustainableagricultural economy

　　C. gaining international support

　　D. converting agricultural land intoforest

　　答案：b

　　36.The Sahel zone is an area which ___.

　　A. is covered with sad and grass

　　B. has a long history

　　C. occupies much of South Nigeria

　　D. belongs to Sudan

　　答案：a

　　37. What is the situation about thedesertification in Africa?

　　A. The deserts are replaced withgrasslands

　　B. The deserts are expanding

　　C. the deserts are moving northwards

　　D. the deserts are being deserted

　　答案：b

　　38. The word “deteriorated ” in paragraph2 means ___.

　　A. deepened

　　B. suffered

　　C. slipped

　　D. worsened

　　答案：d

　　39. What is the root causeof desertification?

　　A. poor farming

　　B. overpopulation

　　C. radical climate change

　　D. disappearance of rare plant species

　　答案：a

　　40. In order to prevent desertification,the author proposes ___.

　　A. making good use of international aids

　　B. developing a sustainableagricultural economy

　　C. gaining international support

　　D. converting agricultural land intoforest

　　答案：b