歷年考研英語(yǔ)閱讀理解1994年04

[00:00.51]1994 Passage4 [00:02.93]"I have great confidence that by the end of the decade [00:06.77]we'll know in vast detail how cancer cells arise," [00:11.41]says microbiologist Robert Weinberg, an expert on cancer. [00:16.86]"But," he cautions, "some people have the idea [00:20.88]that once one understands the causes, [00:23.71]the cure will rapidly follow. [00:26.23]Consider Pasteur. [00:28.15]He discovered the causes of many kinds of infections, [00:31.89]but it was fifty or sixty years before cures were available." [00:37.12]This year, 50 percent of the 910,000 people [00:42.05]who suffer from cancer will survive at least five years. [00:46.60]In the year 2000, [00:48.51]the National Cancer Institute estimates, [00:51.33]that figure will be 75 percent. [00:54.57]For some skin cancers, the five-year survival rate [00:57.90]is as high as 90 percent. [01:00.93]But other survival statistics are still discouraging [01:04.85]--13 percent for lung cancer, [01:07.58]and 2 percent for cancer of the pancreas. [01:11.71]With as many as 120 varieties in existence, [01:15.84]discovering how cancer works is not easy. [01:19.67]The researchers made great progress in the early 1970s, [01:24.31]when they discovered that oncogenes, [01:26.85]which are cancer-causing genes, [01:29.02]are inactive in normal cells. [01:31.85]Anything from cosmic rays to radiation to diet [01:35.88]may activate a dormant oncogene, [01:39.20]but how remains unknown. [01:41.82]If several oncogenes are driven into action, [01:44.85]the cell, unable to turn them off, becomes cancerous. [01:49.58]The exact mechanisms involved are still mysterious, [01:53.72]but the likelihood that many cancers [01:55.94]are initiated at the level of genes suggests [01:59.06]that we will never prevent all cancers. [02:02.39]"Changes are a normal part of the evolutionary process," [02:06.12]says oncologist William Hayward. [02:08.95]Environmental factors can never be totally eliminated; [02:12.37]as Hayward points out, [02:14.08]"We can't prepare a medicine against cosmic rays." [02:18.73]The prospects for cure, though still distant, are brighter. [02:22.34]在線英語(yǔ)聽力室(www.tingroom.com)友情制作 [02:23.24]"First, we need to understand [02:24.88]how the normal cell controls itself. [02:28.31]Second, we have to determine [02:30.13]whether there are a limited number of genes in cells [02:33.05]which are always responsible for at least part of the trouble. [02:37.69]If we can understand how cancer works, [02:40.51]we can counteract its action."

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