When 100 people who have not used cocaine are tested for cocaine use, on average only 5 will test positive. By contrast, of every 100 people who have used cocaine 99 will test positive. Thus, when a randomly chosen group of people is tested for cocaine use, the vast majority of those who test positive will be poeple who have used cocaine.
A reasoning error in the argument is that the argument
(A) attempts to infor a value judgment from purely factual premises
(B) attributes to every member of the population the properties of the average member of the population
(C) fails to take into account what proportion of the population have used cocaine
(D) ignores the fact that some cocaine users do not test positive
(E) advocates testing people for cocaine use when there is no reason to suspect that they hae used cocaine.
Answer(C). but why i think B is right? who can help me?
In my opinion，the key to the question should be （C）。
Pay attention to the premise of the text‘s conclusion：“when a randomly chosen group of people is tested ”，but the premises of the text’s evidence are 5 out of 100 persons，who definately do not use cocaine， and 99 out of 100 people ， who are definately cocaine users。Do you find out the difference now？Good luck！
