四级阅读单选题讲解的内容：句子释义题

四级阅读单选题讲解的内容：句子释义题

　　下面是英语四级阅读单选题讲解：句子释义题。

　　Where do pesticides fit into the picture of environmental disease? We have seen that they now pollute soil，water and food, that they have the power to make our streams fishless and our gardens and woodlands silent and birdless. Man,however much he may like to pretend the contrary,is a part of nature. Can he escape a pollution that is now so thoroughly distributed throughout our world?

　　We know that even single exposures to these chemicals, if the amount is large enough, can cause extremely severe poisoning. But this is not the major problem. The sudden illness or death of farmers， farm-workers,and others exposed to sufficient quantities of pesticides is very sad and should not occur. For the population as a whole，we must be more concerned with the delayed effects of absorbing small amounts of the pesticides that invisibly pollute our world.

　　I Responsible public health officials have pointed out that the biological effects of chemicals are accumulative over long periods of time,and that the danger to the individual may depend on the sum of the exposures received throughout his lifetime. For these very reasons the danger is easily ignored. It is human nature to shake off what may seem to us a threat of future disaster. Men are naturally most impressed by diseases which have obvious signs，，，says a wise physician?Dr. Rene Dubos, yet some of their worst enemies slowly approach them unnoticed.