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历年考研英语阅读理解1994年04

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[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.

[02:23.24]"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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