考研备考的过程漫长而痛苦，在复习中，会遇到很多困难，不少考生付出很多努力却收效甚微，从而产生茫然的失落感；或失去备考的热情与信心。究其原因，无非是考生无法准确找到复习的重点，遇到疑难问题无法得到满意的解答。

　　The history of life on earth has been a history of interaction between living things and their surroundings. To a large extent, the physical form and the habits of the earth's vegetation and its animal life have been molded by the environment. Considering the whole span of earthly time,the opposite effect, in which life actually modifies its surroundings, has been relatively slight. Only in the present century has one species man acquired significant power to alter the nature of his world.

　　During the past quarter century this power has not only become increasingly great but it has changed in character. The most alarming of all man's assaults upon the environment is the contamination of air, earth, rivers, and sea with dangerous and even lethal materials. This pollution is for the most part irrecoverable. In this now universal contamination of the environment, chemicals are the sinister partners of radiation in changing the very nature of the world the very nature of its life. Chemicals sprayed on croplands or forests or gardens lie long in soil,entering into living organisms, passing from one to another in a chain of poisoning and death. Or they pass mysteriously by underground streams until they emerge and combine into new forms that kill vegetation, sicken cattle, and work unknown harm on those who drink from once pure wells. Man can hardly even recognize the devils of his own creation, as a scientist has said.

　　It took hundreds of millions of years to produce the life that now inhabits the earth. Given time not in years but in millennia life adjusts, and a balance has been reached. But in the modern world there is no time.

　　The rapidity of change follows the impetuous pace of man rather than the deliberate pace of nature. Radiation is now the unnatural creation of man's tampering with the atom. The chemicals are the synthetic creations of man's inventive mind, having no counterparts in nature.

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