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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. E. The water in the rural county was brought up to the sanitary standards of the water in neighboring counties ten years ago. B also tends to support the officials’ explanation, because it eliminates a factor that might have differentiated between those contracting and those not contracting the disease and thus rules out an alternative explanation.
答案是C，我是想问一下OG对B的解释，我看得有点云里雾里的。 B说有病的和没病的消耗的瓶装春泉差不多，这个消除了这两类人的差别。但是这个为什么rule out an alternative explanation啊？到底什么东东啊？
谢谢！谢谢！
[此贴子已经被作者于2008-7-27 18:46:07编辑过] | 
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发表于 2008-7-27 18:45:00
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