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. Which of the following is an assumption on
which the argument depends?
A. The dose of tranquilizer delivered by a tranquilizer dart is large enough to give the rangers
putting collars on rhinoceroses a generous margin of safety.
B. The fertility rate of uncollared female rhinoceroses in the park has been increasing in the past
C. Any stress that female rhinoceroses may suffer as a result of being immobilized and handled
has little or no negative effect on their fertility.
D. The male rhinoceroses in the wildlife park do net lose their collars as often as the park’s female
E. The tranquilizer used in immobilizing rhinoceroses is the same as the tranquilizer used in
working with other large mammals.
The conclusion is : some substance in the tranquilizer inhibits fertility.
Negating C means that stress that female rhinoceroses may suffer due to the collars has negative effect on their fertility. Then, the argument will be not valid at all.