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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."
According to the National Cancer Institute estimates, we know that ______.
选项 A、75 percent of cancer patients will survive
B、only 50 percent of people who suffer from cancer will survive
C、90 percent of skin cancers will be cured
D、some cancer patients’ five-year survival rate has been increased but not all
答案D
解析 选项D可以定位到第二段的第二句。前一句说91万人中，50％的癌病患者可以活五年，这一个数据到了2000年增加到了75％，并且皮肤癌的五年存活率高达90％。但是肺癌和胰腺癌的存活率还很低。因此可以得出：有些癌症病人的五年存活率提高了，但不是所有癌症的存活率都提高了。本段当中的三个数据(75％，50％，90％)说的都是癌症的五年存活率，因此选项A、B和C都是偷换概念。
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