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题库 / Prep2008E2-CR-74
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?
Whether there are more collared female rhinoceroses than uncollared female rhinoceroses in the park
How the tranquilizer that is used for immobilizing rhinoceroses differs, if at all, from tranquilizers used in working with other large mammals
How often park rangers need to use tranquilizer darts to immobilize rhinoceroses for reasons other than attaching radio collars
Whether male rhinoceroses in the wildlife park lose their collars any more often than the park's female rhinoceroses do
Whether radio collars are the only practical means that park rangers have for tracking the movements of rhinoceroses in the park
情景：现在这个世道，连犀牛都要安装GPS了。但是，犀牛可不像人一样，不可能老实的让你安装GPS，所以管理员们就必须麻醉犀牛。现在的情况是，凡是被经常麻醉的母犀牛的生育率都比较低，所以结论句为：Some substance in the tranquilizer inhibits fertility。
推理：
前提：recollar（注射麻醉剂）和“生育率低”之间存在正相关关系
结论：某种麻醉剂中的物质阻止了犀牛的生育
答案预估：
其它能解释为何“犀牛生育率低”的原因是否存在。
“某种麻醉剂中的物质阻止了犀牛的生育”的其它必要条件（常理上能保真推理出的一切结果）是否存在。
选项分析：
A选项：在公园中带collar的母犀牛是不是比不带collar的母犀牛要多？无论带collar的母犀牛的绝对数量有多少，都没有提及到生育率低的问题，所以本选项不是答案。
B选项：用于麻醉犀牛的麻醉剂是否和用于其他大型动物身上的麻醉剂有区别？同样地，本选项并没有提到犀牛生育率高低的问题。
C选项：Correct. 除掉佩戴collar这个原因外，公园护林员是否频繁的由于其他原因而麻醉犀牛？这些犀牛的生育率是相对固定的，即recollar的比不recollar的要低一些。如果公园护林员有很多其他原因去麻醉犀牛的话，那么就表示，recollar的犀牛所用的麻醉剂的量并不一定比不recollar的高。反之，如果一般不麻醉其它犀牛，这就是结论的另一个必要条件了。
D选项：在公园中公犀牛是不是比母犀牛更容易弄掉collar？本选项没有提到生育率的问题，可以排除。
E选项：Collar是不是公园护林员追踪犀牛活动的唯一的方法？本选项没有提到生育率的问题，可以排除。
题眼在frequently -> how often
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