完形填空

　　Ecology(生態(tài)學) is a science of how living creatures and plants exist together and develop on each other and on the local government. Where an environment is undisturbed, the ecology of an area is 1 balance, but if a creature dies out or a new species(種類) is 2 then the ecology of an area will be upset, in other 3 , the balance. of nature will be 4 .

　　Man is a part of the 5 and has done more to upset the ecology during 6 short span of time on earth than 7 other creature . He has done this by his ignorance (無知) . his 8 , his thoughtless foolishness and his uncontrolled wastefulness. He has poisoned the 9 and polluted both land and water. He has wasted the earth's natural 10 , with no thought for the future, and has thought out the most devastating ways of killing his fellow men and every other sort of life at the same time.

　　Since man has done so much 11 , it is 12 to man to try to put matters 13 if it is not already too 14 . If there is to be any remedy(補救法) for our ills, that remedy ultimately lies in the hands of the 15 , and the sooner they start doing something about it, the 16 .

　　One of the main 17 of the earth's troubles is that the world is too crowded and that this overpopulation is growing at an ever-increasing rate. At the same time we are 18 up our natural resources — fuels and mineral ores — at an ever-increasing rate with no hope of replacing them.

　　For many years the earth has been unable to 19 enough food for these rapidly expanding population and the position has been steadily getting worse 20 some of our richest soils was lost and vast areas that were once fertile(富饒的) lands were turned into deserts.

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