GMAT PREP good question

lunar wrote:A major chemical spill occurred five years ago at Baker's Beach, the world's sole nesting ground for Merrick sea turtles, and prevented nearly all the eggs laid that year from hatching. Yet the number of adult female Merricks returning to lay their eggs at Baker's Beach has actually increased somewhat since five years ago. Clearly, environmentalists' prediction that the world's Merrick population would decline as a result of the spill has proven unfounded. Which of the following, if true, most seriously undermines the argument offered in refutation of the environmentalists' prediction?

Ok, this argument is pretty straightforward. The environmentalists predicted that the spill would cause a decline in the population of Merricks. The argument seeks to refute that prediction based on the fact that five years later there are more turtles on the beach than there were before the spill.

To undermine that argument, we probably need to show that somehow there could still be a decline going on even though now there are more Merricks on the beach. We don't know how that will work. Maybe these Merricks are from somewhere else, and so there is still a decline but it is not obvious? Maybe the effects of the spill have not shown up yet? Probably, rather than seeking to figure out the answer in advance, the best thing to do at this point is go to the answer choices and find one that works.

A. The chemical spill five years ago occurred at a time when there were neither Merrick sea turtles nor Merrick sea turtle eggs on Baker's Beach.

This may seem somehow relevant, but the argument says that the spill "prevented nearly all the eggs laid that year from hatching." So somehow, even though there were no eggs there when the spill occurred, the spill prevented hatching, and so this answer choice makes no difference.

B. Female Merrick sea turtles begin returning to Baker's Beach to lay their eggs when they are ten years old.

This is interesting, and is probably the right answer. Five years later, there are more adult females than before the spill, BUT, the information in this answer choice makes it clear that the females on the beach five years after the spill were born at least five years before the spill, and females born at the time of the spill would not return for ten years after that, which is five years into the future. So these females we see now were born long before the spill, and therefore their presence does not refute the environmentalists' prediction. (Of all things, the situation is as theorized above; the effects of the spill are not yet obvious.)

C. Under normal conditions, only a small proportion of hatchling female Merrick sea turtles survive in the ocean until adulthood and return to lay their eggs at Baker's Beach.

This is a constant situation and is irrelevant, doing nothing to undermine the argument against the environmentalists' prediction.

D. Environmental pressures unrelated to the chemical spill have caused a significant decline in the population of one of the several species of sea birds that prey on Merrick sea turtle eggs.

This is interesting too, but maybe not as good as B. If birds are not eating as many eggs, then that could explain the population increase. So even though we don't see a decline, in a way the environmentalists could still be right that the chemical spill affected the turtles. At the same time, this does not really undermine the argument, because the population did not in fact decline as the environmentalists had predicted.

E. After the chemical spill, an environmental group rejected a proposal to increase the Merrick sea turtle population by transferring eggs from Baker's Beach to nearby beaches that had not been affected by the spill.

This looks as if maybe it means something, but really it does not. That some eggs may have been saved via their being moved affects neither the accuracy of the environmentalists' prediction made based on what actually happened nor the validity of any argument refuting that prediction.

So B is the best.