An annually conducted, nationwide survey shows a continuing marked decline in the use of illegal drugs by high school seniors over the last three years.
10. Which of the following, if true, casts most doubt on the relevance of the survey results described above for drawing conclusions about illegal drug use in the teen-age population as a whole?
(A) Because of cuts in funding, no survey of illegal drug use by high school seniors will be conducted next year.
(B) The decline uncovered in the survey has occurred despite the decreasing cost of illegal drugs.
(C) Illegal drug use by teen-agers is highest in those areas of the country where teen-agers are least likely to stay in high school for their senior year.
(D) Survey participants are more likely now than they were three years ago to describe as “heroic” people who were addicted to illegal drugs and have been able to quit.（C）
(E) The proportion of high school seniors who say that they strongly disapprove of illegal drug use has declined over the last three years.
Answer: C
D说样本有问题，对象都是三年前成功戒毒的青少年，所以survey的结论有问题。很合适的doubt理由。怎么排除呢？
请大牛们不吝赐教~~~~~~~谢谢！！！
c对毫无疑问
d对样本提出了质疑，但是质疑不对。并没有说戒毒成功的青少年，而是说可能他们现在认为上瘾的人戒掉很牛。。并没有说他们不用药物
所以你认为被调查人群用药变少了，是你自己的臆测，并没有真实证据。
所以D是错误地。。
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