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  3. "I have great confidence that by the end of the decade we’ll know in vast detail how cancer cells arise," says microbiologist Ro

"I have great confidence that by the end of the decade we’ll know in vast detail how cancer cells arise," says microbiologist Ro

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问题     "I have great confidence that by the end of the decade we’ll know in vast detail how cancer cells arise," says microbiologist Robert Weinberg, an expert on cancer. "But," he cautions, "some people may have the idea that once one understands the causes, the cure will rapidly follow. Consider Pasteur. He discovered the causes of many kinds of infections, but it was fifty or sixty years before cures were available."
    This year, 50 percent of the 910 000 people who suffer from cancer will survive at least five years. In the year 2000, the National Cancer Institute estimates, that figure will be 75 percent. For some skin cancers, the five-year survival rate is as high as 90 percent. But other survival statistics are still discouraging—13 percent for lung cancer, and 2 percent for cancer of the pancreas.
    With as many as 120 varieties in existence, discovering how cancer works is not easy. The researchers made great progress in the early 1970s, when they discovered that oncogenes, which are cancer-causing genes, are inactive in normal cells. Anything from cosmic rays to radiation to diet may activate a dormant oncogene, but how remains unknown. If several oncogenes are driven into action, the cell, unable to turn them off, becomes cancerous.
    The exact mechanisms involved are still mysterious, but the likelihood that many cancers are initiated at the level of genes suggests that we will never prevent all cancers. "Changes are a normal part of the evolutionary process," says oncologist William Hayward. Environmental factors can never be totally eliminated; as Hayward points out, "We can’t prepare a medicine against cosmic rays."
    The prospects for cure, though still distant, are brighter. "First, we need to understand how the normal cell controls itself. Second, we have to determine whether there are a limited number of genes in cells which are always responsible for at least part of the trouble. If we can understand how cancer works, we can counteract its action."
Oncogenes become cancerous when they ______.
选项 A、are inactive
B、are activated
C、are becoming cancer-causing genes
D、made great progress
答案B
解析 选项B对应第三段最后一句话，根据这句话，可以看出，癌细胞要进行癌变，条件是致癌基因要被激活(driven into action)，也就是说B选项是同义改写。选项A与B相反，因此是错误的。选项C对应本段第二句中的非限定性定语从句。根据这句话可知，Oncogene本来就是致癌基因，因此致癌基因发生癌变并不是因为他们变成了致癌基因，这是对文意的曲解。选项D对应本段第二句话开头，这里的说明对象是研究者，而不是致癌基因，因此选项D属于偷换概念。
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