Trees are useful to man in three important ways: they provide him with wood and other products;they give him shade;and they help to prevent droughts and floods.
　　Unfortunately, in many parts of the world, man has not realized that the third of these services is the most important.In his eagerness to make money from trees, he has cut them down inlarge numbers, only to find that without them he has lost the best friends he had. And besides, he is usually too caless to plant and look after new trees.So the forests slowly disappear.
　　This does not only mean that man will have fewer trees.The results are even more serious: for where there are trees, their roots break up soil--allowing the rain to sink in--and also bind the soil, thus preventing it from being washed away easily;but where there are no trees, the ran falls on hard ground and flows away, causing floods and canting away the rich top-soil.When all the top-soil is gone, nothing remains but worthless desert.
　　Two thousand years ago a rich and powerful country cut down its trees to build warships, with which to gain itself an empire.It set up the empire but, without its trees, its soil became poor and it grew weak.
　　When the empire fell to pieces, the home country found itself faced with floods and starvation.
　　16.What is the most important service of trees to man according to the passage?
　　A.They help him make money
　　B.They give him wood and other products
　　C.They help him prevent droughts and floods
　　D.They give him shade
　　答案：C
　　17.Why do forests in many parts of the world slowly disappear?
　　A.New trees are not looked after properly
　　B.Many trees have been cut down by man
　　C.Man has nol paid enough attention to planting trees
　　D.All of the above
　　答案：D
　　18.Why did the country mentioned in the passage suffer from floods and starvation?
　　A.Because an empire was set up
　　B.Because the empire fell to pieces
　　C.Because it lost its trees
　　D.Because too much had been spent on wars
　　答案：C
　　19.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.Because roots of the trees break up the soil
　　答案：B
　　20.What does the author tell us in this passage?
　　A.How trees help prevent droughts and floods
　　B.The relationship between trees and man
　　C.How an empire fell to pieces in ancient times
　　D.A story of trees
　　答案：A

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