Where do pesticides (杀虫剂) 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 contrary, is 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 are 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.
Responsible public health officials have pointed out that the biological effects of chemicals are cumulative (积累的) 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."
16. Which of the following is closest in meaning to the sentence "Man, ...is part of nature." (Para.1)? [A] Man appears indifferent to what happens in nature. [B] Man acts as if he does not belong to nature. [C] Man can avoid the effects of environmental pollution. [D] Man can escape his responsibilities for environmental protection.
17. What is the author's attitude to wards the evnironmental effects of pesticides? [A] Pessimistic. [B] Indifferent. [C] Defensive. [D] Concerned.
18. In the author's view, the sudden death caused by exposure to large amounts of pesticides ______. [A] is not the worst of thenegative consequences resulting from the use of pesticides [B] now occurs most frequently among all accidental deaths [C] has sharply increased so as to become the center of public attention [D] is unavoidable because people can't do without pesticides in farming
19. People tend to ignore the delayed effects of exposure to chemicals because ______. [A] limited exposure to them does little harm to people's health [B] the present is more important for them than the future [C] the danger does not become apparent immediately [D] humans are capable of withstanding small amounts of poisoning
20. It can be concluded from Dr Dubos' remarks that ______. [A] people find invisible diseases difficult to deal with [B] attacks by hidden enemies tend to be fatal [C] diseases with obvious signs are easy to cure [D] people tend to overlook hidden dangers caused by pesticides
contrary, is part of nature. Can he escape a pollution that is now so thoroughly distributed throughout our world? 
