macattack wrote:Please Help

Dear macattack,
I'm happy to help with this.

First of all, this is an "evaluate the argument" question. Here's a blog about this particular question type:
https://magoosh.com/gmat/2013/gmat-criti ... onclusion/

Here's the argument again:
Lyme disease is caused by a bacterium transmitted to humans be deer ticks. Generally, deer ticks pick up the bacterium while in the larval stage by feeding on infected white-footed mice. However, certain other species on which the larvae feed do not harbor the bacterium. If the population of these other species were increased, more of the larvae would be feeding on uninfected hosts, so the number of ticks acquiring the bacterium would likely decline.
So, very specifically, we want to know about this plan --- increase the number of "other species", and would this increase the number of non-infected ticks? --- is this a feasible plan?

(A) Whether populations of other species on which deer tick larvae feed are found only in areas also inhabited by white-footed mice.
The word "only" should make us suspicious right away. Suppose the answer to this were "no" --- suppose some of these other species were found as far away as Alaska or Mongolia. How would this impact the credibility of the argument in the least? The plan is to increase their population, which would result in increasing them right here, where the white-footed mice is. If they also increase in other places on the planet, that's irrelevant. (A) is incorrect.

(B) Whether the size of the deer tick population is currently limited by the availability of animals for the tick's larval stage to feed on.
Very interesting. Suppose something else, anything else, were limiting the deer tick population. Then if we increased the number of "other species" animals, that wouldn't increase the deer tick population, because the other thing, whatever it is, would still be holding the population in check. That would destroy this particular plan. This is highly relevant, so pending review of other answers, this looks like a very promising answer choice.

(C) Whether the infected deer tick population could be controlled by increase the number of animals that prey on white-footed mice.
This is an entirely different plan. For the larger question of how to combat Lyme Disease, this could be useful, but our job is not to evaluate this larger question. We are quite specifically focused on evaluating this plan in particular. Whether another, totally different plan would be successful does not shed any light on whether this plan will be successful. (C) is incorrect.

(D) Whether deer ticks that were not infected as larvae can become infected as adults by feeding on deer on which infected deer ticks have feed.
Interesting. If the answer to this is "yes", then the total number of infected ticks right now would reflect the amplification of this "feedback loop". Even if this is true, if we could cut the number/percent of deer ticks infected in the larval phase, then fewer ticks would infect deer, and fewer other ticks would be infected by feasting on infected deer. Even if this amplification process were still involved, if we cut the input number, the output number will still drop. In other words, whether the answer to this is "yes" or "no", it doesn't fundamentally change whether the proposed plan would be successful. (D) is incorrect.

(E) Whether the other species on which deer tick larvae harbor any other bacteria that ticks transmit to humans.
This would be relevant if our concern were human health overall. That's a BIG concern. If we were employees of the Center for Disease Control, this would be a relevant concern. BUT, our concern, quite specifically, is evaluating this plan, a plan about controlling the spread of deer tick infected with the Lyme Disease bacterium. Whether other bacteria are also in the mix does not affect whether this particular plan will be successful. (E) is incorrect.

We have eliminated four answers, so the only possible answer is (B), the OA.

Does this make sense?
Mike