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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.
【C5】
选项 A、mostly
B、partially
C、sometimes
D、rarely
答案C
解析 本句破折号后举例说明维生素的组成成分：碳、氢、氧和______氮，and表明各成分之间为并列关系，选项应与usually相呼应。usually是频度副词，选项也应是频度副词。mostly和partially不是频率副词，而是强调事物部分与整体的关系，rarely是频率副词，但它含否定含义，若用于句中，之前的连词and应改为表示转折关系的but。故选C。
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