填空题

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, ________ do they construct or build any part of the body. They are needed for ________ foods into energy and body maintenance. There are thirteen or more of them, and if ________ is missing a deficiency disease becomes ________ . 　　Vitamins are similar because they are made of the same elements―usually carbon, hydrogen, oxygen, and ______ nitrogen. They are different ______ their elements are arranged differently, and each vitamin ______ one or more specific functions in the body. 　　 ________ enough vitamins is essential to life, although the body has no nutritional use for ________ vitamins. Many people, ________ , 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.