[求助]不明白！

muller

A recent survey of all auto accident victims in Dole County found that, of the severely injured drivers and front-seat passengers, 80 percent were not wearing seat belts at the time of their accidents. This indicates that, by wearing seat belts, drivers and front-seat passengers can greatly reduce their risk of being severely injured if they are in an auto accident.
The conclusion above is not properly drawn unless which of the following is true?
(A) Of all the drivers and front-seat passengers in the survey, more than 20 percent were wearing seat belts at the time of their accidents.
(B) Considerably more than 20 percent of drivers and front-seat passengers in Dole County always wear seat belts when traveling by car.
(C) More drivers and front-seat passengers in the survey than rear-seat passengers were very severely injured.
(D) More than half of the drivers and front-seat passengers in the survey were not wearing seat belts at the time of their accidents.
(E) Most of the auto accidents reported to police in Dole County do not involve any serious injury.
答案是A，可是我怎么觉得A就是原文所给的信息取非啊？那位大侠帮我分析分析！谢谢！

dorbear

单纯80%和20%的重伤比例并不必然说明不系安全带重伤几率就大，关键还要知道不系安全带重伤的人数占事故中所有不系安全带人数的比例。比如说事故中不系安全带的人占90%，系安全带的人占10%，这时重伤人数80-20%的比例缺德出相反的结论。

答案A的确是得到一个余集，但目的是要取得一个最低的比例关系。

muller