大学英语四级阅读理解练习 二

Directions: There are 4 passages in this part. Each passage is followed by some questions or unfinished statements. For each of them there are four choices marked A), B), C) and D). You should decide on the best choice and mark the corresponding letter on the Answer Sheet with a single line through the centre.
Questions 1 to 5 are based on the following passage:
In the warm enclosed water of farm ponds, conditions are very likely to be lethal for fish when insecticides（杀虫剂）are applied in the neighbourhood. As many examples show, the poison is carried in by rains and runoff from surrounding lands. Sometimes the ponds receive not only polluted runoff but also a direct dose as crop-dusting pilots neglect to shut off the duster in passing over a pond. Even without such complication, normal agricultural use subjects fish to far heavier concentrations of chemicals than would be required to kill them. In other words, a marked reduction in the amount used would hardly change the fatal situation, for application of over 0.1 pound per acre to the pond itself are generally considered hazardous. And the poison, once introduced, is hard to get rid of. One pond that had been treated with DDT to remove unwanted shiners（银色小鱼）remained so poisonous through repeated draining and washing that it killed 94% of the sunfish with which it was later stocked. Apparently the chemical remained in the mud of the pond bottom.
　　In some parts of the world the cultivation of fish in ponds provides an indispensable source of food. In such places the use of insecticides without regard for the effects on fish creates immediate problems. In Rhodesia, for example, the young of an import food fish, the Kafue bream（鲷科海鱼）, are killed by exposure to only 0.04 parts per million of DDT in shallow pools. Even smaller die, of many other insecticides would be fatal. The shallow waters in which these fish live are favorable mosquito-breeding places. The problem of controlling mosquitoes and at the same time conserving a fish important in the Central African diet has obviously not been solved satisfactorily.
　　1. The word "lethal" in the first sentence nearly means ________.
　　 A) dead
　　 B) important
　　 C) fatal
　　 D) vital
　　2. The author's tone in this passage can be best described as ________.
　　 A) depressed
　　 B) indifferent
　　 C) questioning
　　 D) objective
　　3.________ should be responsible for the presence of insecticides in ponds?
　　 A) Rhodesia
　　 B) Central Africa
　　 C) Conditions of farm ponds
　　 D) Human error
　　4. The author states a problem, ________ , and relates causes in this passage.
　　 A) gives examples
　　 B) proposes a solution
　　 C) explains his suggestion
　　 D) makes speeches
　　5. Which of the following titles best sums up the whole passage?
　　 A) The Effect of Insecticides on Fish
　　 B) The Water of Farm Ponds
　　 C) The Cultivation of Fish as Food
　　 D) Saving African Food Supplies