(C) says, "Wolf packs in the region with the declining moose population generally prey on only moose and deer, but in the neighboring region the wolf packs prey on a wider variety of species."
This is a tricky choice, but we have to keep in mind that we're looking to resolve the paradox of why the deer were a relevant factor in the moose population's decline in one region but didn't have an effect on the moose population in another region. This answer might help us to explain why more moose didn't live in one region, but it fails to explain why the deer were to blame for this. (C) puts the blame on wolves. The important discrepancy in the stimulus is about how relevant the deer were to the deaths of the moose. Thus, (C) fails to help us resolve this conflict. As a result, we can get rid of this answer choice.
Does this make sense? Let us know if you have any other questions!