2. 考研
  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

admin2015-01-15  18
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 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 Haywar. 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 are cancer-causing genes______.
选项 A、that are always in operation in a healthy person
B、which remain unharmful so long as they are not activated
C、that can be driven out of normal cells
D、which normal cells can’t turn off
答案B
解析 从第3段第2句“在20世纪70年代初，研究者们取得了很大进步，当时他们发现在正常细胞中，致癌基因并不活跃。从宇宙射线到辐射饮食等任何东西都可能激活休眠的致癌基因，但如何维持这种状态还不为人知。如果几个致癌基因被激活，而细胞不能将它们消灭，则会成为癌细胞”可知，B项为正确答案。
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