Hi akhilsuhag,

This is a really specifically-worded prompt and I bet that many Test Takers would get this question wrong. It's based on 'causality' (the idea that one thing causes another), but he key to solving it is in the way that the last part of the last sentence is worded: "so the NUMBER of ticks....will likely decline."

The Facts:
-Lyme Disease is caused by a bacterium transmitted by deer ticks to humans.
-Deer ticks generally get this disease when they're in the LARVAL STAGE by feeding on infected white-footed mice.
-Larvel deer ticks feed on OTHER species though (that do NOT have the disease)

The Conclusion:
-IF the populations of those OTHER species are increased, then more of the deer ticks will feed on those other species, so the NUMBER of infected deer ticks would DECLINE.

The Logic:
When dealing with 'causal' arguments, you have to assume that everything else stays the same - in that way, you'll know that "X causes Y." Here, we have to assume that the existing deer tick population will stay the same. If so, then if more of those deer ticks are feeding on NON-infected animals, then the NUMBER of infected deer ticks would logically decrease. HOWEVER, if the introduction of a new food source INCREASES the number of deer ticks, then it's possible that the TOTAL NUMBER OF INFECTED deer ticks would NOT decrease (the ratio might decrease, but not necessarily the NUMBER). The only answer that focuses on all of these details (larval deer ticks, increasing food source, NUMBER of infected deer ticks) is B

GMAT assassins aren't born, they're made,
Rich