请大家帮忙解答~~~多谢多谢!!!

想问问大家

39. 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

答案我不是特别能理解, 其他选项我都能排除

还有一题

48. Millions of identical copies of a plant can be produced using new tissue-culture and cloning techniques.

If plant propagation by such methods in laboratories proves economical, each of the following, if true, represents a benefit of the new techniques to farmers EXCEPT

A. The techniques allow the development of superior strains to take place more rapidly, requiring fewer generations of plants grown to maturity.

为什么不选A?

试解答：

39 出车祸的100人中有80人没系安全带。A给的是开车的1000人中大于200（我们假定250）人系了安全带。所以系安全带发生车祸几率低于不系安全带，虽然这个数字不是significant。

48 这项技术是为了治疗损伤，而不是为了“可以治疗而去故意增加损伤”。就像国家有监狱是为了减少某些人对社会的危害，而不是为了“可以更加是无忌惮地危害社会”。

我后来又想了想

严重受伤的人里面,80%是没系安全带的,20%是系了安全带的

结论给的是wearing seat belt can reduct their risk of being severely injured if they are in an auto accident.

那它的前提条件必须得是所有系安全带的认数高于20%,才能说明系安全带比较安全,比如说有50%的人系安全带,其中20%的人受伤.

48题好象解释的....

我是不太明白为什么"requiring fewer generations of plants grown to maturity"会是一个benefit?