大全-2-14

liaokangyu

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.
(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 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.

答案是a，但為什麼不能選d呢?

robertchu

"More than half" in D is ambiguous, as 51% is more than half, as well as 99%.  Consider these:

If 51% of all the surveyed were not wearing seat belts, then 49% of the surveyed were wearing.  Since folks wearing seat belts made only 20% of those severely injured, this indicates that wearing seat belt reduces the risk of being severely injured – it supports the original argument.

However, if 99% of the surveyed were not wearing, then 1% of the surveyed were wearing.  Because folks wearing made 20% of those severely injured, this indicates that those wearing seat belt have more chance of getting severely injured -- it weakens the original argument.