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.

19.   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

(C) 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）

(E) figures for the cigarette industry as a whole and may not hold for a particular company

看了以前的解释还是不明白，有NN能帮忙详细解释一下吗?为何选E?

举个极端的例子，有一些公司20%的gross receipts用于promotion in magazines，却抢到了0%的烟民；另一些公司对promotion in magazines完全没有投入，却抢到了20%的烟民......那么平均一下，还是10%的gross receipts用于promotion in magazine，抢到了10%的烟民。：）

整体和个体的问题。