Because of the lucrative but illegal trade in rhinoceros horns, a certain rhinoceros species has been hunted nearly to extinction.
Therefore an effective way to ensure the survival of that species would be to periodically trim off the horns of all rhinoceroses, thereby eliminating the motivation for poaching.
Which one of the following is an
assumption required by the argument?
(A) Most poachers who are discouraged from hunting rhinoceroses are not likely to hunt other animals for their horns. -> If other animals are being hunted, then how can it is related to the survival of rhinoceros. Irrelevant.
(B) At lease some rhinoceroses whose horns are periodically trimmed off will be able to attract mates. -> It looks off to me at first. Let's think deeper, if some rhinoceroses attract mates, then they won't get extinct. This is the answer, we were looking for. It makes sense. Let's keep it.
(C) Poachers hunt at lease some immature rhinoceroses whose horns have not yet started to develop. -> Irrelevant.
(D) The demand for rhinoceros horns will remain constant even if the supply decreases after the periodical trimming-off of the rhinoceros horns has begun -> demand remains constant doesn't answer how rhinoceroses won't extinct after the periodical trimming-off of horns. Incorrect.
(E) Rhinoceroses whose horns have been trimmed off are unable to defend themselves against predators. -> Then Rhinoceroses will be extinct easily, they won't be able to defend themselves. It is weakening the argument. Incorrect.
So, I think B.