请教NN一道逻辑题：关于汽车事故的

昨天就写了几句中文，结果被某位gg说懒，今天改邪归正，把题好好的答下来，希望nn帮忙看下。。。。

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

A就是正确答案了 其他的有明显错误就不用打了吧.....老师说，加not削弱，可是我感觉是加强啊。还有其他的方法吗？谢谢~~~~~~