新prep1-74

74.   (29534-!-item-!-188;#058&004138)

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C， 请问NN怎么理解， 谢谢！！！！

C.How often park rangers need to use tranquilizer darts to immobilize rhinoceroses for reasons other than attaching radio collars

We are told that there must be a causal  relationship between low fertility rates with  recollared  female rhinoceroses and a tranquilizer dart used, in frequent putting back
            the slipped collar. To unswer this, we need to find the relationship between tranquilizer and putting back collars.

To convince and evaluate it,  we need to prove that  a tranquilizer is more frequently used in putting back the collars ( attaching radia collars) rather than immobilize rhinocernoses,thus we can come to the causal relationship :  low fertility is cased by attaching collars when it is more frequent in attaching collars rather than immobilize..