chesstitans wrote:

In a certain state, the rate at which inhabitants of City X contract a certain disease is significantly lower than the rate at which inhabitants of City Y contract the disease. So if a couple originally from City Y relocates to City X and raises a family there, their children will be significantly less likely to contract this disease than they would had they remained in City Y.

Which of the following, if true, would most seriously weaken the conclusion drawn in the passage?

A) Many health experts do not believe that moving to City X will lead to a significant increase in the average person’s immunity to the disease.

B) The mayor of City Y has falsely claimed that statistics relating to the incidence of the disease in his city are not accurate.

C) The lower incidence of the disease in City X can be ascribed mostly to genetically determined factors.

D) Some inhabitants of City Y possess a greater immunity to the disease than do the healthiest inhabitants of City X.

E) Smog levels in City X are significantly lower than those of any other city in the state.

KAPLAN OFFICIAL EXPLANATION:

C

To weaken the argument, we need to find the choice that contradicts its key assumption. The conclusion is that moving from City Y to City X will lower the likelihood of contracting the disease, since the disease occurs at a much lower rate in City X. The assumption is that the fact of being born in or living in City X reduces the risk of contracting the disease; in other words, environmental factors (such as lifestyle, air quality, health care costs, or some other factor affecting people's lives) in City X are responsible for the low incidence of the disease. Now let's find a choice the makes this assumption unlikely to be true.

(A) is out of scope; the rates of incidence in the two cities, not the opinion of professionals, are at issue here. Also, this type of "appeal to authority" is rarely correct on the GMAT. (B) would strengthen the argument; the statistics state that the incidence is higher in City Y and if the mayor were proven to have falsely suggested otherwise, it would still make sense to move to City X, where the incidence is lower. (D) is irrelevant. Even if true, it would not imply that the risk for the average person is lower in City Y.

(E) is out of scope; we have no information on whether smog has anything to do with the disease in question. Furthermore, this would, if anything, strengthen the conclusion by

providing at least one sense in which City X is a more healthful place to live. (C) states that genetic makeup (as opposed to something in the environment) is responsible for the low incidence of the disease in City X. In other words, the risk is determined by genetic factors, not by where one is born or where one lives. This contradicts the assumption that there is something about the environment in City X that lowers the risk of contracting the disease, so (C) is correct.

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