跪求大神指点一道prep逻辑题

GloriaCCC

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.
在野生动物园，管理员可以通过一个无线电收发器跟踪犀牛的移动，但是这个东西经常掉。为了安置上去必须把犀牛用麻醉枪打昏。那些经常被装上这些装置的母犀牛比没装的生育率低。可见麻醉剂阻碍生育。问假设？
B. The fertility rate of uncollared female rhinoceroses in the park has been increasing in the past few decades.
C. Any stress that female rhinoceroses may suffer as a result of being immobilized and handled has little or no negative effect on their fertility.
答案选C  
我看了两个版本的解析，一个说C中的any stress may suffer指的是由于被麻醉而带来的紧张不会给犀牛的生育率带来不好的影响
    另一个说除了麻醉剂，打昏和其他压力对于生育没影响
如果是前者的话，那不是削弱了？。。还有B说uncollared的生育率就高，不是有加强的作用吗。。。？为什么不对呢。。     谢谢啦！！！！  ：）））

刚劲小职员

C选项中的是说紧张，并不是substance导致的，所以是排除他因，所以还是假设。

刚劲小职员

C选项中的是说紧张，并不是substance导致的，所以是排除他因，所以还是假设。
另外，B中的uncollared生育率高，是无关选项，不能说明collared怎样，更不能说明collared中的substance的作用。