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  3. Insects have inhabited the earth for well over 300 million years, and during that time they have evolved into an almost unbeliev

Insects have inhabited the earth for well over 300 million years, and during that time they have evolved into an almost unbeliev

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问题     Insects have inhabited the earth for well over 300 million years, and during that time they have evolved into an almost unbelievable variety of species. The astronomical numbers involved in any discussion of the insect world are difficult for the imagination to grasp. There are probably more than a million different species of them, compared with a mere 20,000 species of all other animals, and according to the best estimates roughly 1,018 individual insects are living at any given time.
    Most insects are completely harmless to man, and many are directly beneficial. Only about one-tenth of one percent of the insect world consists of species harmful to man, but throughout human history these have been a persistent threat. Many infectious diseases are transmitted to man by insects. Perhaps even more important, insects are man’s principal competitors(indeed his only serious competitors)for food. Nearly 40 percent of the world’s food crops is destroyed by insects each year.
    The battle against harmful insects has been fought for thousands of years, but man has never gained more than a transitory advantage. Whenever man has concentrated in significant numbers and practiced any form of agriculture, the insect population has inevitably risen because man’s crops and domesticated animals have provided a rich source of food for them. Efforts to reduce or eliminate harmful insect populations are on record from as far back as 1, 000 B. C. An uneasy balance has occasionally been abandoned to the insects in hopes that the remaining yield would be sufficient for human needs. Whenever various circumstances, including man’s own mismanagement of the environment, have upset this balance and allowed the insect population to explode, the result has been a graphic demonstration of man’s inability to attain mastery over insects.
    The methods employed to control the growth of undesirable insects can be classified as biological, chemical, cultural, reproductive, mechanical and physical control.
    None of the above types of control, used by itself, has ever proved to be more than a temporary solution to the insect problem, but an integrated approach utilizing combinations of these methods can keep insect populations down to a point where farming remains economical. No method, however, offers any hope that unwanted insects will ever be eliminected altogether.
According to the passage, there are probably more than______different species of insects.
选项 A、1, 018
B、20,000
C、a million
D、300 million
答案C
解析 细节事实题。根据题干关键词different species of insects与原文首段第三句中重现，进行定位。题干中的probably more than与原文重现，因此其后的a million即为答案。故答案为C。
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