[求助]急，这题该怎么做？

happypoor88

这题为什么选C呢？我觉得B对啊，感染和未感染的人引用的水量无明显区别，不就说明了水没有问题吗？不就削弱了原题吗？为什么解释中却说B选项是加强了原题呢？

29. The number of people diagnosed as having a certain intestinal disease has dropped significantly in a rural county this year, as compared to last year. Health officials attribute this decrease entirely to improved sanitary conditions at water-treatment plants, which made for cleaner water this year and thus reduced the incidence of the disease.

 

Which of the following, if true, would most seriously weaken the health officials’ explanation for the lower incidence of the disease?

A. Many new water-treatment plants have been built in the last five years in the rural county.

B. Bottled spring water has not been consumed in significantly different quantities by people diagnosed as having the intestinal disease, as compared to people who did not contract the disease.

C. Because of a new diagnostic technique, many people who until this year would have been diagnosed as having the intestinal disease are now correctly diagnosed as suffering from intestinal ulcers.

D. Because of medical advances this year, far fewer people who contract the intestinal disease will develop severe cases of the disease. C

E. The water in the rural county was brought up to the sanitary standards of the water in neighboring counties ten years ago.

tommytang

这题应该选C,派出他因。因为题目中的结论是water-treatment plants的sanitary condition改善了，所以被诊断出intestinal disease的人比去年减少了，要weaken这个推理，就要找出其它能够导致确诊为intestinal disease的人降低的理由，而C说由于诊断技术的发展导致以前被诊断出intestinal disease的人很多其实都没有得intestinal disease。

tommytang

B说被诊断得了intestinal disease的人比没有得intestinal disease的人少饮用矿泉水，这说明饮用矿泉水不容易得病，而饮用自来水则容易得病，从而自来水厂卫生条件的改善是可以导致intestinal disease的人降低的，所以是增强而不是减弱。

gonghao

OG上的题，楼主反复读解释会明白的。