20-119 Scientists have discovered the importance of social and ecological factors to epidemics. Polimyelitis, for example, emerged as an epidemic in the United States in the twentieth centry; by then moder sanitation was able to delay exposure to polio untill adolescence or adulthood, at which time polio infection produced paralysis. Previously, infection had occured during infancy, when it typically provided lifelong immunity without paralysis. Thus the hygiene that helped prevent typhoid epidemics indirectly fostered a paralytic polio epidemic. 119. The passage suggests that a lack of modern sanitation would make which of the following most likely to occur? C an epidemic of typhoid D an epidemic of paralytic polio among infants E an epidemic of paralytic polio amnong adolesents and adults. the answer is C. 根据前面的话可以看出，后面P的例子是用来支持社会和生态因素对EPIDEMIC有影响的。但是这个例子，我不太理解。怎么忽然从BECAUSE句里蹦出来个T EPIDEMIC? 最后一句说现代医学对T和防治导致了P的发生，怎么导致的？前面并没有表明二者有什么联系啊？ 选项C其实并没有什么不对，但是很容易被忽略，因为此例看上去是针对P的。所以直观的判断应该是关于P的。但是可能是因为DE不对吧，但是为啥呢？ | 
