单选题Why does land become desert after all trees are cut down?A Because nothing remains on land except floods.B Because there are no longer trees to keep the rain and protect the top-soil.C Because too much rain sinks in and washes away the top-soil.D Becau

共用题干
Why Buy Shade-Grown Coffee?
When people argue about whether coffee is good for health,they're usually thinking of the health of the coffee drinker. Is it good for your heart?Does it increase blood pressure?Does it help you concentrate?However,coffee affects the health of the human population in other ways, too.
Traditionally,coffee bushes were planted under the canopy（树冠）of taller indigenous（土生土长的）trees. However, more and more farmers in Latin America are deforesting the land to grow full-sun coffees.At first,this increases production because more coffee bushes can be plan- ted if there aren't any trees.With increased production come increased profits.
Unfortunately,deforesting for coffee production immediately decreases local wildlife habitat Native birds nest and hide from predators（捕食者）in the tall trees and migrating birds rest there.
Furthermore,in the long term,the full-sun method also damages the ecosystem because more chemical fertilizers and pesticides are needed to grow the coffee.The fertilizers and pesti- cides kill insects that eat coffee plant,but then the birds eat the poisoned insects and also die. The chemicals kill or sicken other animals as well,and can even enter the water that people will eventually drink.
Fortunately,farmers in Central and South America are beginning to grow more coffee bushes in the shade.We can support these farmers by buying coffee with such labels as“shade grown” and“bird friendly.”Sure,these varieties might cost a little more.But we're paying for the health of the birds,the land,ourselves,and the planet. I think it's worth it.

How do farmers find more land for growing full-sun coffee?
A: They buy more land from other farmers.
B: They cut down trees.
C: They move to another country.
D:.They turn grassland into farmland.

After many years' wandering all over the world,the man finally settled down to the business his father left to him.

A:focused on
B:depended on
C:insisted on
D:dwelled on

Deforestation and Desertification(沙漠化)
　　The Sahel zone lies between the Sahara desert and the fertile savannahs(热带大草原)of northern Nigeria and South Sudan. The word sahel comes from Arabic and means marginal or transitional ,and this is a good description of the semi-arid(半干旱) lands, which occupy much of the Western African countries of Mail, Mauritania, Niger ,and Chad.
　　Unfortunately, over the last century the Sahara desert has steadily crept southwards eating into once productive Sahel lands. United Nations surveys show that over 70 percent of the dry land in agriculture use in Africa has deteriorate dover the last 30 years. Droughts have become more severe, the most recent lasting over twenty years in parts of the Sahel region. The same process of desertification is taking place across southern Africa as the Kalahari desert advances into Botswana and parts of South Africa.
　　One of the major causes of this desert advance is poor 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 supplies are exhausted. Over cultivation一 trying to grow too many crops on poor land一 results in the soil becoming even less fertile and drier, and beginning to break up. Soil erosion (侵蚀) follows, and the land turns into desert.
　　Another cause of desertification is loss of tree cover. Trees are cut down for use as fuel and to clear land for agricultural use. Tree roots help to bind the soil together, to conserve moisture, and to provide a habitat for her plants and animals. When trees are cut down, the soil begins to dry and loosen, wind and rain erosion increase, other plant species die, and eventually the fertile top soil may be almost entirely lost, leaving only bare rock and dust.
　　The effects of loss of topsoil and increased drought are irreversible. They are, however, preventable. Careful conservation of tree cover and sustainable agricultural land use have been shown to halt deterioration of soils and lessen the 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)agricultural economy. This may be a model for similar projects in other West African countries.
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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