Bunuel wrote:

The plastics commonly used in household garbage bags take, on average, 100 years to decompose in landfills. From an environmental standpoint, the plastic bag industry should be forced to switch to newly developed plastics, which begin to decompose after only 20 years.

Which of the following pieces of information would be most helpful in evaluating the argument above?

(A) the rate of growth or decline in sales of plastic garbage bags

(B) the number of plastic garbage bags sold last year that eventually wound up in landfills

(C) the feasibility of enforcing legislation that regulates the plastics used in garbage bags

(D) the length of time it takes the newly developed plastic to fully decompose in landfills.

(E) a comparison of the production cost of one bag made with the old plastics and of one bag made with the new plastics

KAPLAN OFFICIAL EXPLANATION:

Some questions test nothing more than whether you've recognized a scope shift, and this one falls into that category. The question stem complicates matters, however, and requires a bit of translation. A piece of information that would help us evaluate the argument is essentially a piece of information that would strengthen or weaken the argument. The right choice will need to have one of those effects in order for us to be able to say that this argument is good or bad. In other words, the operative question the student has to ask himself to test each choice is: "Does this help me pass judgment on the argument?" Such evaluations are common in GMAT Critical Reasoning.

An 800 test taker interprets question stems in the light of how they instruct him to deal with the passage.

Now, if you picked up on the scope shift, then you would have known that the right choice will somehow address it. The shift is subtle, but definite, and perhaps if you didn't see it up front on your own, you would have recognized the shift when you came to correct choice (D). The author argues for the switch to the new plastics, but takes no account of the fact that there's a disparity in the information given. The newly developed plastic takes only 20 years to begin to decompose, but we need to know how long it takes for it to fully decompose in landfills before we can pass judgment on the argument. Only then would we be able to compare the new plastics to the current bags. (D) provides this information and is therefore correct.

(A) and (B) present irrelevant issues. We're trying to evaluate whether the change from one plastic to another is environmentally beneficial.

Neither of these pieces of information helps us to differentiate between the environmental impact of the old vs. new bags.

(C) Whether or not the industry will be able to switch over to and legally maintain the new plastic bags is outside the scope. The question is whether or not it should.

An 800 test taker understands that when an argument is based around the notion that something "should" be done, whether or not it "can" be done is logically irrelevant.

(E) offers up an irrelevant distinction. The argument is made from an environmental standpoint; the cost per bag has no logical bearing on this.

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