In some ways, the human body is both like a furnace and like an engine. It must have fuel to produce heat as a furnace【C1】______. It must have fuel to produce motion and do【C2】______as an engine does. The nutrients(营养物)which【C3】______energy best are carbohydrates(碳水化合物)and fats. Protein can also be used as fuel. Minerals, vitamins, and water,【C4】______extremely valuable to the body, cannot be used as fuel. If the body takes in more carbohydrates【C5】______are used for energy, the【C6】______is stored. Two storage places are the liver(肝)and muscles. There is a【C7】______, however, to the amount of carbohydrates they can【C8】______. When they are filled and they always【C9】______be for you to feel your best, excess carbohydrates are changed to fat and【C10】______around the body. If the body does not take【C11】______a sufficient amount of food, it will use its stored fat for energy. If you【C12】______at all, the body would use up all the stored fats and【C13】______it would use its own protein in order to keep【C14】______as long as possible. Therefore, the【C15】______amount of food you eat should be in【C16】______with your energy requirements. It is not necessary,【C17】______, for you to go【C18】______counting calories(卡路里)and weighing food. If a person is the【C19】______weight, it is safe to【C20】______that he is eating enough. 【C1】