请教一道PREP题

rucstarchan

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
B. How the tranquilizer that is used for immobilizing rhinoceroses differs, if at all, from tranquilizers used in working with other large mammals
C. How often park rangers need to use tranquilizer darts to immobilize rhinoceroses for reasons other than attaching radio collars
D. Whether male rhinoceroses in the wildlife park lose their collars any more often than the park’s female rhinoceroses do
E. Whether radio collars are the only practical means that park rangers have for tracking the movements of rhinoceroses in the park

答案是C。不太明白，请大家帮忙解答~~

yknxhdsy

首先分析一下题干：
背景信息：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.动物园的管理人员要在犀牛身上安装一种collar来记录犀牛的活动。如果collar滑掉了，还要再按上。
Evidence：
Putting a collar on a rhinoceros involves immobilizing the animal by shooting it with a tranquilizer dart.  安装collar要打镇定剂。
Female rhinoceroses that have been frequently recollared have significantly lower fertility rates than uncollared females。又被重新安装collar的母犀牛的生育能力比没有安装collar的生育能力低。
Conclusion：
probably，some substance in the tranquilizer inhibits fertility。镇静剂影响生育能力。

这类问题是逻辑里常见的归因问题。
X→Y，一般的weaken题里，常见的weaken项有Y→X，或者Z→Y。

这里evaluate 因果关系，也要从这两个方向入手。
这道题，看选项，只有选项C，在讨论是否有其他的原因会影响到母犀牛的生育能力。C选项问，除了要安装 radio collar 这种情形之外，使用镇静剂的频率是多少。答案是很少的话，很有可能镇静剂不足以导致生育能力下降，存在其他原因；答案是很多的话，说明有可能（probably，原文结论里包含这个词），镇静剂导致生育能力降低。
所以正确答案是C

billsq

二楼回答的太精辟了

rucstarchan

明白了。谢谢@！！@