第二节 完型填空
阅读下面短文，从短文后所给各题的四个选项(A、B、C和D)中选出能填入相应空白处的最佳选项。
Of all living creatures on earth, insects are the most plentiful. Some 【B1】 are very useful to man, for example, bees, 【B2】 which we get honey, and silkworms(蚕) ,which 【B3】 us silk. Other varieties, however are extremely 【B4】 , and do a great amount of 【B5】 , especially to crops. Locusts (蝗虫) are perhaps the most dangerous of all, 【B6】 they will eat almost any green 【B7】 'and when millions of them 【B8】 on cultivated land(耕地)they soon 【B9】 it bare (光秃秃的). In some countries they are the farmer's 【B10】 enemy. Another annoyance is the common 【B11】 ,not only because it Worries us indoors and out-of-doors, but because it 【B12】 diseases.
Scientists have given much time and 【B13】 to the study of insects. It needs the most careful and 【B14】 observation. Thanks to their discoveries we now 【B15】 almost all that there is to be known 【B16】 the habits of these hardworking insects, bees and ants, which live in 【B17】 better, planned in some ways than our 【B18】 society. But the most valuable work has been done in trying to give 【B19】 to men, animals and crops from the 【B20】 which insects cause.
【B1】

A. members
B. varieties
C. qualities
D. forms