请教一题：PREP CR1 74

liulu007

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
为什么是c，请指教？

genius1824

我觉得是不是可以这样理解：
文中最后一句的意思是试图表述：用来稳定犀牛的镇定剂中可能含有某种物质使得母犀牛生育下降。而c的意思是：巡山员在不是为了重新安装雷达探测器的原因下而使用镇定剂稳定母犀牛的频率有多少？（意思没写的太清楚，潜在的意思其实就是说可能有担心镇定剂使得母犀牛生育下降的顾虑，巡山员可能会减少镇定剂的使用）
不知道这样解释是否清楚？

overdrivewang

还是不明白啊。。。。额。。。如果use tranquilizer darts for other reasons often, 就否认了结论：tranquilizer inhibits fertility。。。不管是不是其他原因会多用tranquilizer。。这个对于结论的前提条件Female rhinoceroses that have been frequently recollared have significantly lower fertility rates than uncollared females. 没有什么影响啊。。。求解释。。。

SiyangWu

从题目可知radio collars经常脱落的rhinoceroses需要tranquilizer dart来使它immobile，然后recollared，这个时候就会用到tranquilizer。
但是如果uncollared female 还会在其他情况下也用到tranquilizer，那么在这种情况下，可能项圈经常滑落并需要tranquilizer的和项圈不经常滑落（该处不要用tranquilizer）但是其他原因要用tranquilizer的，他们两个都用了同量的tranquilizer，所以量上没有区别，这就不能证明tranquilizer inhibits fertility.
所以How often park rangers need to use tranquilizer darts to immobilize rhinoceroses for reasons other than attaching radio collars很重要。如果use tranquilizer darts for other reasons often, 就否认了结论：tranquilizer inhibits fertility。如果只有当需要带项圈时用到tranquilizer，这可证明结论是有理的。

啰嗦了

applemay

还是不明白啊。。。。额。。。如果use tranquilizer darts for other reasons often, 就否认了结论：tranquilizer inhibits fertility。。。不管是不是其他原因会多用tranquilizer。。这个对于结论的前提条件Female rhinoceroses that have been frequently recollared have significantly lower fertility rates than uncollared females. 没有什么影响啊。。。求解释。。。


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