请教一道逻辑题！！！

ogmat

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 reat-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.
A): A   why? [CXD: p254, 30]

StephanieYun

这是一道数学比例的题目。选项成立时题目的结论才会成立。
题目的结论是: 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. , 题目给出的条件是: among the severely injured drivers and front-seat passengers , more than 80% were not wearing seat belts at the time of their accidents. 要有这个条件就说明结论的成立显然有缺陷。 选项正是补充这个deficiency. while at the same time, from the point of view of demonstration, the question belongs to the kind of rate-question. That is , by comparing two rates , which are depicting the severeness of two groups among the survey, the author could logically infer that by wearing seat belts, drivers and front seat passengers could greatly reduce their risk of being severely injured. What is said in choice A would be the one rate which is compared to the one in the argument.








生活是一杯清茶

ogmat

谢谢斑竹的回复！
可是我还没怎么看懂，：P
尤其对20％的比例不理解，
您能说清楚一点吗？
麻烦您了！

crane_gh

这道题 应该是考假设  
原题说 调查表明 受伤的人里 有 80%人 没有系安全带  因此推出 系安全带 有利于 前排人降低危险
可以看出 两部分人是不同的  一部分是 受伤的人  一部分是 全体的前排人
题中隐含的假设应该是   受伤的人 的这个比例 可以代表总体前排人的 比例
因此 此题的选项应该是   受伤中没系安全带的比例可以代表总体前排人不系安全带的比例  选项一 既是说明 总体中前排不系安全带的比例 也不低于 80%