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英语六级考试模拟试卷含答案(9)

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    Vitamin D is made by the body when exposed to sunlight and is stored in the muscles, however, if the skin is rarely exposed to the sunlight or is dark little vitamin D is produced. Foods such as eggs and oily fish are all rich in vitamin D.
   
    Vitamins K
   
    Vitamin K, phylloquinone, is found in dark green leafy vegetables such as spinach and kale. It is a fat soluble vitamin which is involved in the clotting process of blood. In the intestines bacteria synthesize a number of important clotting factors which need vitamin K. Without vitamin K cuts can fail to heal and internal bleeding can occur.
   
    Vitamins C
   
    Vitamin C is a water soluble vitamin, known chemically as ascorbic acid. It is found in citrus fruits such as oranges and lemons, and also in potatoes and tomatoes. The main function of vitamin C is the formation of connective tissues such as collagen. It is also known to be an antioxidant which helps to remove toxins and aids the immune system. A lack of vitamin C leads to Scurvy, a condition experienced by sailors on long journeys when they did not have fruit in their diets. Scurvy causes painful, bleeding gums. As vitamin C is water soluble, it is not toxic in high doses as it can be excreted in the urine, very high doses can however cause diarrhea.
   
    Vitamins B
   
    B group vitamins have a wide range of roles acting as co-enzymes in metabolic pathways. They are found in most plant and animal tissues involved in metabolism, therefore foods such as liver, yeast and dairy products are all rich in B group vitamins. Deficiency of B group vitamins include dermatitis, fatigue and malformation of red blood cells.
1. An adult needs about 12,000kJ of energy a day from ________.
   
    A. the cell
   
    B. the respiring process of carbohydrates
   
    C. fats in the cell
   
    D. a balanced diet
   
    2. Carbohydrates are ultimately absorbed into cells in the process of _______.
   
    A. digestion
   
    B. respiration
   
    C. oxidization
   
    D. mobilization
   
    3. The Essential Amino Acids which build part of proteins can be obtained from______.
   
    A. stomach
   
    B. body tissues
   
    C. the body
   
    D. the diet
   
    4. The ultimate cause of kwashiorkor is lack of ________.
   
    A. protein
   
    B. carbohydrates

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