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  3. Too much metal in the soil is considered pollution. Yet too little metal in a person’s diet can cause health problems. An Americ

Too much metal in the soil is considered pollution. Yet too little metal in a person’s diet can cause health problems. An Americ

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问题    Too much metal in the soil is considered pollution. Yet too little metal in a person’s diet can cause health problems. An American scientist says the answer to both problems may be plants that take up large amounts of metal in their tissues.
   David Salt is an expert on plants at Purdue University in West Lafayette, Indiana. He is working with plants that store large amounts of metals.
   In recent years, scientists have shown interest in using such plants to clean up harmful waste materials, Professor Salt says such plants also could be used to improve people’s diets or even to create foods that fight cancer.
   Humans need a number of metals in their diets, including iron and zinc. These metals are needed in very small amounts, however. That is why they are called micronutrients. The lack of micronutrients is blamed for health problems in many developing countries. Children and pregnant women are mostly affected.
   Recently, Mr. Salt announced that he has identified and copied the genes from a kind of plant that stores metals in its tissues. He says his study suggests it may be possible to develop plants that contain minerals needed for good health.
   For example, the metal selenium is a strong anti-cancer agent. Some wild plants store selenium naturally. Mr. Salt says foods to fight cancer might be created if genes from these plants could be moved into crop plants.
   Locoweed, which is a common plant in the western U. S., stores selenium. Professor Salt says it may be possible to create cancer-fighting foods from it. He and scientists from a company called Unicycle Therapies have copied the gene that causes locoweed to take up selenium from the soil.
   Many people take pills to add important minerals or vitamins to their diet. However, Mister Salt notes that most selenium products sold in health food stores are of little use. That is because the human body can only take in and use selenium if it is in the right chemical form.
   The scientist says his team would like to develop a vegetable crop high in selenium. He wants to create an anti-cancer product in the foods we already eat.
选项 A、clean polluted soil and cure disease like cancer
B、clean up harmful waste materials in soil and improve people’s diet
C、produce large number of micronutrients such as iron and zinc
D、create food with important minerals or vitamins
答案B
解析 文章首段即讲到美国的一位科学家，即下文中的David Salt，认为这样的植物可以用来解决两方面的问题——净化土壤和促进人类健康。
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