美国英语听力80篇1 Lesson20
20)Sweet Potato Project
Lack of Vitamin A is the leading cause of blindness among children in deveoping countries.
These children do not get enough Vitamin A in the food they eat.
In Africa,more than 3,000,000 children suffer from blindness or sickness caused by lack of Bitamin A.
Scientists say sweet potatoes are rich in beta carotene--the natural orange-colored substance 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 supervised the ten-year study.
The scientists found that several kinds of sweet potatoes produce excellent harvests in some areas where Bitamin A deficiency 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 acceppt such potatoes because they are sweeter than locally-grown sweet potatoes.
The traditional African sweet potato is white and contains little or no beta-carotene.
However, research studies and taste tests showed the new sweet potatoes are able to compete with the local crops.
Wanda Collins is a research official 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 shortages caused price increases.
Ms.Collins says the next step is to develop this important crop in other areas of Africa.
The International Potato Center reports that many women and girls in southern and eastern Africa grow sweet potatoes.
The crops are grown on small pieces of land used to produce family food supplies.
African farmers produce almost 7;000,000 tons of sweet potatoes each year.
However, the production rate is only about five tons per hectare.
In all developing countries, the average production rate is fifteen tons per hectare.
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