14. 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.无关，对象有差异
(C) More drivers and front-seat passengers in the survey than rear-seat passengers were very severely injured.无关比较对象
(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.（A）
(E) Most of the auto accidents reported to police in Dole County do not involve any serious injury.无关
请问D为何不对啊
D讲调查中一半以上的司机和前排乘客没有带安全带 结果造成重伤的占80%
也支持了结论了
我的想法哪里不对呢
谢谢
The conclusion above is not properly drawn unless which of the following is true?
我认为这题应该是问assumption吧!!
对
我认为D也行啊
The conclusion above is not properly drawn unless which of the following is true?
requires a necessary condition for the conclusion already established.
同意楼上的看法
所以D是非必要的 因为原文给的理由是80 percent were not wearing seat belts at the time of their accidents
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
D取非 More than half of the drivers and front-seat passengers in the survey were wearing seat belts at the time of their accidents
对结论影响不大 A才是桥梁
题目问的是假设 要求的是必要条件
我将A取非
Of all the drivers and front-seat passengers in the survey, more than 20 percent were not wearing seat belts at the time of their accidents.
假设有90%的人没有带安全带 重伤中80%的人 没有带安全带
也没有削弱结论啊
请大家帮助 谢谢
题目问的是假设 要求的是必要条件
我将A取非
Of all the drivers and front-seat passengers in the survey, more than 20 percent were not wearing seat belts at the time of their accidents.
假设有90%的人没有带安全带 重伤中80%的人 没有带安全带
那就无法知道安全带是不是个会降低重伤的因素
也就是无法得到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
D是干扰选项；(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.
原文说的是A recent survey of all auto accident victims，of the severely injured drivers and front-seat passengers, 80 percent were not wearing seat belts at the time of their accidents调查的是所有的受害人；而说的是重伤的司机和乘客当中，80％没系安全带。所以有没有D并不影响原文的结论。
A正确可以用集合来解释原文，所有的受调查者看成一个集合的话，那么重伤的最大就是调查者这个集合一样大，那么也就是这种情况下是80％没系安全带，20％系了安全带就是最少的情况了。
D是干扰选项；(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.
原文说的是A recent survey of all auto accident victims，of the severely injured drivers and front-seat passengers, 80 percent were not wearing seat belts at the time of their accidents调查的是所有的受害人；而说的是重伤的司机和乘客当中，80％没系安全带。所以有没有D并不影响原文的结论。
A也是
调查的是所有的受害人；而说的是重伤的司机和乘客当中，80％没系安全带。
可是A是答案
A是正确的，受重伤的人这个集合最大的情况就是所有的受调查者既all auto accident victims ，这时候80％没系安全带，那么还有20％系安全带，从此可以推出至少有20％系了安全带的。
D之所以不对，是因为受重伤的乘客可能只是受调查者的一小部分，那么有没有一半以上没系安全带就不影响结果了。
如果这20％系了安全带的in the severely injured drivers and front-seat passengers 就等于或小于所有in all auto accident victims in Dole County 系了安全带的 那是不是表示安全带无法降低severely injured 的情形 所以必须大于20%
这样讲不知有没有比较清楚?
安全带的效用＝（被调查的用安全带的人－用了安全带而受重伤的人）/被调查的用了安全带的人。
从这个公式就可以推出A答案了。
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