第四部分：阅读理解（第31~45题，每题3分，共45分）
下面有3篇短文，每篇短文后有5道题。请根据短文内容，为每题确定1个最佳选项
第一篇
Genetic Engineering
Genetic engineering began when the DNA molecule(分子), the most basic unit of life, was first described in 1953 by James Watson and Francis Crick. An understanding of DNA led to the altering of normal cell reproduction. Experiments with altering human cells began in 1970. In one of the first experiments, patients were injected with a virus that would produce a life-saving enzyme, but their bodies would not accept it. In 1980 patients with a rare but fatal blood disease were injected with a purified gene that was cloned through DNA technology. Another failure.
Genetic engineering got a legal boost(激励) in 1980. The U.S. Supreme Court said that a patent could be granted on a genetically engineered oil-eating bacterium(细菌). This bacterium would help clean up oil spills. The ruling encouraged companies to invent new life forms, and three important medical products were quickly developed.
l Human interferon(干扰素)-- a possible solution to some cancers and viral disease. A newly engineered bacterium produced human interferon as a by-product. This new product reduced the cost of interferon.
l Human growth hormone-- for children whose bodies do not grow to normal height. An expensive growth hormone(荷尔蒙) was previously produced from human cadavers, but by changing the genetic make-up of the single-cell bacterium E. coli, and affordable growth hormone could be produced.
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