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CR question (Cigarette smokers)

以下的題目我能理解正確答案是E的原因,但我想知道為什麼C 不正確。

Surveys show that every year only 10 percent of cigarette smokers switch brands. Yet the manufacturers have been spending an amount equal to 10 percent of their gross receipts on cigarette promotion in magazines. It follows from these figures that inducing cigarette smokers to switch brands did not pay, and that cigarette companies would have been no worse off economically if they had dropped their advertising.

Of the following, the best criticism of the conclusion that inducing cigarette smokers to switch brands did not pay is that the conclusion is based on

(A) computing advertising costs as a percentage of gross receipts, not of overall costs
(B) past patterns of smoking and may not carry over to the future
© the assumption that each smoker is loyal to a single brand of cigarettes at any one time
(D) the assumption that each manufacturer produces only one brand of cigarettes
(E) figures for the cigarette industry as a whole and may not hold for a particular company

There is never such an assumption like “C” mentioned. It is totally compatible with the possibility that one smoker has 2 or more brands - just 10% of them switch to others.