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  3. Lack of Vitamin A is the leading cause of blindness among children in developing countries. These children do not get enoug

Lack of Vitamin A is the leading cause of blindness among children in developing countries. These children do not get enoug

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问题     Lack of Vitamin A is the leading cause of blindness among children in developing countries.
    These children do not get enough Vitamin A in the food they eat.
    In Africa, more than 3,000,000 children【B1】______blindness or sickness caused by lack of Vitamin A Scientists say sweet potatoes are rich in beta carotene(β-胡萝卜素)—the natural orange-colored【B2】______ that the human body needs to produce Vitamin A.
    One recent study found that orange-colored sweet potatoes are an excellent food for families in southern and eastern Africa. Scientists from Kenya, Uganda and the International Potato Center in Peru【B3】______ the ten-year study. The scientists found that several kinds of sweet potatoes produce excellent harvests in some areas where Vitamin A【B4】______ is widespread. They said sweet potatoes provided large amounts of Vitamin A at a very low cost.
    People in Africa liked the orange-colored sweet potatoes used in the study. Some people had thought Africans would not accept such potatoes because they are sweeter than 【B5】______ sweet potatoes. The traditional African sweet potato is white and 【B6】______ little or no beta-carotene. However, research studies and taste tests showed the new sweet potatoes are able to【B7】______ the local crops. Wanda Collins is a research【B8】______ at the International Potato Center. She says the study found that mothers in Africa accepted the orange-colored sweet potatoes. Women who knew the value of these potatoes continued to buy them when food【B9】______ caused price increases. Ms. Collins says the next step is to develop this【B10】______ crop in other areas of Africa.
【B3】
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答案supervised
解析 此空需填入谓语部分，构成完整的主谓宾结构(Scientists supervised the ten-year study)。supervise“指导”，依据行文时态可知是过去式，词尾勿忘加-d。
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