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  3. Vitamins are organic compounds necessary in small amounts in the diet for the normal growth and maintenance of life of animals,

Vitamins are organic compounds necessary in small amounts in the diet for the normal growth and maintenance of life of animals,

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问题     Vitamins are organic compounds necessary in small amounts in the diet for the normal growth and maintenance of life of animals, including man.
    They do not provide energy, 【C1】______do they construct or build any part of the body. They are needed for【C2】______foods into energy and body maintenance. There are thirteen or more of them, and if 【C3】______is missing a deficiency disease becomes【C4】______.
    Vitamins are similar because they are made of the same elements—usually carbon, hydrogen, oxygen, and【C5】______nitrogen. They are different【C6】______their elements are arranged differently, and each vitamin【C7】______one or more specific functions in the body.
    【C8】______enough vitamins is essential to life, although the body has no nutritional use for 【C9】______vitamins. Many people, 【C10】______, believe in being on the "safe side" and thus take extra vitamins. However, a well balanced diet will usually meet all the body’s vitamin needs.
【C1】
选项 A、either
B、so
C、nor
D、never
答案C
解析 选项必须既能引导倒装句，又能与前面的否定相呼应。either表示“也”，可以用在否定句中，但一般放在句尾；so可以引导倒装句，但它用在肯定句中，表示“也”，nor也可以引导倒装句，并可用在否定句中，构成not．．．nor…(既不……也不……)固定结构，never也可以引导倒装句，表示否定，但它必须放在句首。故选C。
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