英语六级阅读理解练习附详解:医疗技术

　　This year, 50 percent of the 910,000 people who suffer from cancer will survive ai least fiveyears. 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 survivalstatistics are still discouraging-13 percent for lung cancer. and 2 percent for cancer of thepancreas(胰腺)。

　　With as many as 120 varieties in existence, discovering how cancer works is not easy. Theresearchers madegreat progress in the early 1970s. when they discovered that oncogenes.which are cancer-causing genes (基因), are inactive in normal cells. Anything from cosmic raysto radiation to diet may activate a dormant oncogene. but how remains unknown. If severaloncogenes 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 areinitiated ai the level of genes suggests that we will never prevent all cancers. "Changes are anormal pan of the evolutionary process." says oncologist William Hayward. Environmentalfactors can never be totally eliminated; as Hayward points out, "We can't prepare a medicineagainst cosmic rays. "

　　The prospects for cure.though still distant, are brighter.

　　"First we need io understand how the normal cell controls itself. Second,we have todetermine whether there are a limited number of genes in cells which are always responsiblefor al least pan of the trouble. If we can understand how cancer works. we can counteract itsaction."

　　“我很有把握，到本年代末，我们会非常详细地了解到癌细胞是如何产生的，”癌症专家、微生物学家罗伯特·温伯格说。[1]“但是，”他警告说，“有些人认为，一旦有人找到了病因，治疗方法马上就随之而来了。想想巴斯德吧!他发现了许多种感染的原因，但是五六十年后才找到治疗方法。”

　　今年，患癌症的91万人中，有50%至少可以活5年。国家癌症研究所估计，到2000年，这个比例将上升到75%。在患某些皮肤癌的人中，5年存活率高达90%。但是其他癌症患者中能活5年的人所占比例仍令人沮丧——肺癌为13%，胰腺癌为2%。

　　[2]因为已发现的癌症种类多达l20种，要找出癌症是如何发生的并不容易。20世纪70年代初，研究人员取得了重大进展。他们发现，致癌基因——诱发癌症的基因——在正常细胞中不活跃。任何因素，包括宇宙射线、辐射、饮食，都可能激活不活跃的致癌基因。但激活的机制尚无人知晓。[3]如果几个致癌基因被激活，细胞无法将其阻断，就发生癌变。

　　其中确切的机制仍是一个谜，但一种可能性是，许多种癌症是从基因层次开始的，这说明，我们将永远无法防止所有的癌症发生。“进化过程中发生变化是很正常的事，”肿瘤学家威廉·海沃德说。[4]环境因素永远也无法彻底消除;正如海沃德指出的，“我们无法制出药物来防止宇宙射线。”

　　治疗方法前景虽然还很渺茫，但毕竟乐观一些了。

　　“首先，我们必须弄清楚，正常细胞如何自我控制。其次，我们得确定，是不是至少有部分麻烦总是由细胞中数量不多的一些基因所致。[5]如果我们能弄清楚癌症是如何起作用的，我们就可以抑制其活动。”

　　1.Robert Weinberg warns that the discovery of the causes or cancer cells won't necessarily leadto_______________________.

　　2.It is not easy to rind out how cancer works because__________________.

　　3.Once oncogenes in cells are at work.the cell will become_______________________.

　　4.By saying "We can't prepare a medicine against cosmic rays", William Hayward implies that itis impossible to avoid che impact of_______________________.

　　5.Provided that the mechanisms of cancer are found out we are ableto_______________________.

　　1.[the rapid discovery of its cure]