Let's look at the argument. The stimulus tells us that almost all rabies cases come from rabid animal bites, and bats carry rabies. Bats are shy animals that rarely bite, and the overwhelming majority do not have rabies. Thus there is little justification for health warnings that urge the removal of any bats in occupied buildings.
We are looking for a statement that would weaken this argument.
(B) tells us that rabid bats are less mobile but are much more aggressive. This fact suggests that (a) rabid bats that reside in buildings are unlikely to move voluntarily, and (b) they are more likely to act aggressively and bite people even though healthy bats rarely bite. These facts weaken the argument that health warnings urging the removal are unjustified.
(C) adds support to one of the premises in the stimulus - that bats, as one of the animal species that carry rabies - under normal conditions rarely bite people. Thus, (C) actually strengthens rather than weakens the conclusion.
Let me know if this makes sense and if you have any other questions.