Understanding the argument -
Conclusion - Tranquilizer inhibits fertility. Because - Female rhinoceroses that have been frequently recollared have significantly lower fertility rates than uncollared females. Park rangers need to tranquilize rhinoceros to put collars back.
We see a causal connection in the conclusion. Tranquilizer (cause) inhibits fertility (effect).
We need to evaluate the argument - In evaluation, we check the validity of the argument. The correct answers are framed along the lines of assumptions. Let us see what assumption here.
So, how do we weaken the causal argument X causes Y? X but not Y. This means we have Tranquilizer, but it doesn't inhibit fertility. There can be 2 cases. One case using Tranquilizer for recollar: we already know this. Another one is Using Tranquilizer for other than recollar. So, as discussed earlier, correct answers are framed along the lines of assumptions. The assumption here is that the Tranquilizer is not used for something else. We ask whether we use the Tranquilizer for something else. If it's Yes, then it means the conclusion is less valid, but if it's no, then the conclusion is strengthened.
There is another way to weaken the cause and effect. What if there is an alternate cause, Z, that is causing infertility? So, the assumption here is there is no other cause. And as Evlaute questions are framed along the lines of assumptions. So the evaluation question will be: Is there any alternate cause that causes infertility in the recollared females?
So, there are multiple ways to ask the evaluation question once we understand the argument.
Option Elimination -
(A) Whether there are more collared female rhinoceroses than uncollared female rhinoceroses in the park. This is a classic trap. The Argument talks about "rate," and this option talks about the numbers. Distortion.
(B) How the tranquilizer that is used for immobilizing rhinoceroses differs, if at all, from tranquilizers used in working with other large mammals - Other large mammals? Out of scope.
(C) How often park rangers need to use tranquilizer darts to immobilize rhinoceroses for reasons other than attaching radio collars - This is okay as it asks for other uses of tranquilizer. GMAT has made the language complicated to understand.
(D) Whether male rhinoceroses in the wildlife park lose their collars any more often than the park’s female rhinoceroses do - We are comparing female rhinoceroses and their fertility. Out of scope.
(E) Whether radio collars are the only practical means that park rangers have for tracking the movements of rhinoceroses in the park - For now, radio collars are the scope. Other practical means are out of scope.