This is C. Use yes-no question technique

In a certain wildlife park, park rangers are able to track the movements of many rhinoceroses because those animals wear radio collars. When, as often happens, a collar slips off, it is put back on. Putting a collar on a rhinoceros involves immobilizing the animal by shooting it with a tranquilizer dart. Female rhinoceroses that have been frequently recollared have significantly lower fertility rates than uncollared females. Probably, therefore, some substance in the tranquilizer inhibits fertility.
In evaluating the argument, it would be most useful to determine which of the following?

A. Whether there are more collared female rhinoceroses than uncollared female rhinoceroses in the park -->If yes, no influence. If no, no influence
B. How the tranquilizer that is used for immobilizing rhinoceroses differs, if at all, from tranquilizers used in working with other large mammals -->If yes, no influence. If no, no influence
C. How often park rangers need to use tranquilizer darts to immobilize rhinoceroses for reasons other than attaching radio collars -->the best. If yes, it weakens that why only recently collared rhinos have lower fertility rates, because recently uncollared rhinos can still be injected tranquillizer for other reasons, so they can be equally affected as are collared rhinos. If no, it does strengthen the argument
D. Whether male rhinoceroses in the wildlife park lose their collars any more often than the park’s female rhinoceroses do -->If yes, no influence. If no, no influence
E. Whether radio collars are the only practical means that park rangers have for tracking the movements of rhinoceroses in the park -->If yes, strengthen ? If no, it does have a reason to weaken. However, it's not so strong as C, because it doesn't mean park rangers will inject something to rhino's body. They can use an outside-the body effect to track the rhino's movement so that rhinos's fertility is not affected