求教一道题... 新PREP里面的

silviahelena

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.  utting 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.  robably, 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


答案被我隐藏，用反选可见： c

多谢！

pinkking

我是用排除法做的，答案选C。自己想了会也没想出很好的解释，去看了海外论坛别人的解释，忽然明白了，先贴下他们的解释

the best way to "justify" the oa here is to eliminate the other answers. this is more straightforward than on many other problems, because ALL of the wrong answers are VERY much outside the argument's scope.

(a) irrelevant, as the numbers of collared vs. uncollared rhinos are irrelevant to fertility rates (presumably measured in babies per rhino, or # of copulations required per pregnancy, or some other figure that doesn't have anything to do with the total population size).

(b) irrelevant; the argument deals only with rhinos.

(d) irrelevant; the argument deals only with FEMALE rhinos.

(e) irrelevant; the purpose of the collar doesn't affect the fertility issue. moreover, other means of tracking the rhinos lie outside the scope of the argument.

--

that leaves (c).

the reason (c) matters is because the study purports to cover the differences between rhinos that have been hit with tranquilizer darts (let's call them "tranks") and those that haven't. however, the study DOESN'T directly split the rhinos into "trank" and "non-trank" groups; it splits them into "frequently recollared" and "not frequently recollared" groups.
the argument therefore depends on the assumption that "frequently recollared" is an adequate proxy for "been hit by tranks" and that "not frequently recollared" is an adequate proxy for "not been hit by tranks".
choice (c) is very much relevant to this assumption, because that association falls apart if the rhinos are getting tranked for lots of other reasons in addition to the collar issue.

but again, the wrong answers are easy pickings here, so you probably don't even need to think this much.

--

the real question is whether the rhinos can pop their collars.
;)

pinkking

这种题目就是要看分类。题目分类是掉项圈的犀牛和不掉项圈的犀牛，作者的assumtion就是，不掉项圈的犀牛就很少被打麻醉枪，但是有可能不是这样子的。比如麻醉枪在平时也会使用，有可能这两种犀牛平时都经常被打，那么就不能说明麻醉枪和生育率有关了。所以需要这个来取非。

chenmy1991

好題啊