陈向东的gre, gmat lsat-2道题？

P101/18

US ad agencies are increasingly using interviews at shopping malls, called mall intercepts, to test for ad effectiveness, product concept viabillity, and consumer buying habits. Critics of mall intercepts maintain that the shopping habits of mall shoppers are not representative of those of the larger population.

Which of the following would provide evidence that most supports the critics’ claim about mall intercepts?

A, some mall shoppers patronize more than one store in any given shopping trip.

B, Mall shoppers, on average, spend 50 percent more time shopping than shoppers at other locations do.

The key is B, but I choose A, my reason is the same person could be interviewed more than one time if he patronize more than one store, so he can’t represent others, but himself.

But have no clue of B??? any idea?

P110/36

There is a great deal of geographical variation in the frequency of many surgical procedures-up to tenfold variation per hundred thousand between different areas in the numbers of hysterectomies, prostatectomies, and tosillectomies.

To support a conclusion that much of the variation is due to unnecessary surgical procedures, it would be most important to establish which of the following?

B, the variation is unrelated to factors (other than the surgical procedures themselves) that influence the incidence of diseases for which surgery might be considered.

The key is B, but no quite sure the line of reasoning in it, thanks in advance.

can anyone here can help?

A is not right, because it is also possible for shoppers who shop outside of mall patonize the same store more than once. Whereas, B eliminates this possibility and claims that the population of the mall shoppers is not representative.

I am not sure if this is right. Hope this is helpfull