请教各位一道逻辑题：

a recent survey of all auto accident victims in Dole County found that, of the severely injured drivers and front-seat passengers, 80% 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% of drivers and front-seat passengers in Doel Conunty always wear seat belts when travelling 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 fron-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 conuty donot involve any serious injury

题目出自新东方补充教材逻辑39题。

我还是有些不解为什么选A。

题目是说：受重伤的人中有80％没系安全带，换句话说，就是受重伤的人中有20％是系安全带的。

A说：在被调查的人中，超过20％的人在出事时系了安全带。

我实在看不出这两者间有什么联系。请指点。

I think that the statement show that less than 20% person who wear belt is injured , only if the person who wear belt in subvey is more than 20% that means wear belt is more safy than unwear