Trees are useful to man in three very important ways: they provide him wood and other products; they give him shade; and they help to prevent drought (干旱) and floods.Unfortunately, in many parts of the world, man has not realized that the third of these services is themost important. In his eagerness to draw quick profit from the trees, he has cut them down in largenumbers.Two thousand years ago, a rich and powerful country cut down its trees to build warships, withwhich to gain itself an empire. It gained the empire but, without its trees, its soil became bare and poor.When the empire fell to pieces, the country found itself faced by floods and starvation.
Even where a government realizes the importance of a plentiful supply of trees, it is difficultsometimes to make the people realize this. They cut down the trees but are too careless to plant andlook after new trees. So, unless the government has a good system of control, or can educate thepeople, the forests slowly disappear.This does not only mean that there will be fewer trees. The results are even more serious: for wherethere are trees, their roots break the soil up, allowing tile rain to sink in, and also bind the soil. Thisprevents the soil from being washed away. But where there are no trees, the rain falls on hard groundand flows away on the surface, and this causes floods and the rain carries away the rich topsoil inwhich crops grow. When all the topsoil is gone, nothing remains but worthless desert
16. Trees are useful to man mainly in three ways, the most important of which is thatthey can________.A. keep him from the hot sunshineB. enable him to build warshipsC. make him draw quick profit from themD. protect him from droughts and floods
17. It.s a great pity that_______.A. man is only interested in building empiresB. man is eager to profit from treesC. man hasn.t realized the importance of trees to himD. man hasn.t found out that he has lost all trees
18. Sooner or later the forests will disappear_______.A. unless a country has a plenty supply of treesB. unless people stop cutting down their treesC. unless all people are taught the importance of planting treesD. unless tile government punishes those who cut trees instead of planting them
19. The word "bind" ill Paragraph 5 means"__________".A. to wash away B. to make wetC. to make slay together D. to improve
20. When there is a heavy rain, trees can help to prevent floods, as they can______.A. keep rain from falling down to soft groundB. cause the soil to allow rainwater to sink inC. prevent the soil from being washed awayl). make the topsoil stick together

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