Hi umeshpatil,

This is an evaluation question. The author is making an argument that will leave out a central, necessary assumption; we, as test takers, must identify the question that best enables us to judge the validity of the assumption.

The editorial's conclusion is in the first sentence: Metropolis should protect its economy by ditching Costmart. The evidence in support of the conclusion is a statistic: local retailers go bankrupt 20% more frequently when Costmart opens up.

There are two major missing pieces from this argument, and both of them are classic GMAT patterns. The first is representativeness. Whenever you see a statistic or sample, you have to ask yourself if it is really representative of whatever we're concluding about. The author assumes that Metropolis will be affected by Costmart in a manner similar to other cities. The second is unexplored alternatives. That author says that, because of a single bad effect, the city should avoid Costmart. He fails to consider that there might be trade-offs to Costmart, and that some other benefit from Costmart might offset the bankruptcy rate.

So, we look for an answer that addresses one of our two assumptions. The correct answer will either ask, "Is there anything about Metropolis that makes it particularly less susceptible to damage from Costmart?" or "Are there any benefits to a Costmart that might offset the increase in local bankruptcies?"

(C) matches that second prediction perfectly. It's the correct answer. If the answer is "yes," then the author's claim is weakened because he doesn't weight those benefits against the cost, but if the answer is "no" then the editorial is strengthened, because there are no benefits to doing what the author says to avoid.

For the record, (A) and (B) are totally irrelevant to the prompt. (D) doesn't tell us whether a high bankruptcy rate is more or less likely to increase even further, so it isn't a useful question. And (E) is misleading, since "exclusively" is too strong a word and since it's not clear that hiring a large number of potentially minimum-wage part-time jobs would be a benefit regardless.

Thank you sir for clear and concise elaboration. OA is (C).
There is similar example in OG-12, I applied the similar reasoning and chose option (D), which was wrong. Now, I understand as you said 2 facts can be searched to answer similar examples: 1.representativeness 2. unexplored alternatives.
I guess below OG question can be answered by first missing piece i.e. representativeness.

Community acitivist: If Morganville wants to keep its centrals hopping district healthy, if should prevent the opening of a huge SaveAll discount department store on the outskirts of Morganville. Records from other small towns show that whenever SveAll has opened store outside the central shopping district of a small town, within five years the town has experienced the bankruptcies of more than a quarter of the stores in the shopping district.
The answer to which of the following would be most useful for evalutating the community activist's reasoning?
a. Have community activists in other towns successfully campaigned against the opening of a SveAll store on the outskirts of their towns?
b. Do a large percentage of the residents of Morganville currently do almost all of their shopping at stores in Morganville?
c. In towns with healthy central shopping districts, what proportaion of the stores in those districts suffer bankruptcy during a typical five-year period?
d. What proportion of the employees at the SaveAll store on the outskirts of Morganville will be drawn from Morganville?
e. Do newly opened SaveAll stores ever lose money during their first five years of operation?

Note the difference between these two--the official problem has a fixed percentage (a quarter) while the original post had a relative percentage (20% more). Subtle distinctions like that can completely transform the logic behind a problem!