PREP12 PACK1题目

lainemai

Prep2012-Pack1-SC-064 VSC002625 hard

　　Although beavers can still be found throughout the western United States, their number has declined compared with the eighteenth century, when the abundance of beavers lured armies of European trappers into the Rocky Mountain region to slaughter them for their pelts.

　　A. their number has declined compared with

　　B. their numbers have compared with

　　C. their numbers have declined since

　　D. their numbers have in comparison to those of

　　E. the number of them declined since

答案选择C，我想问为什么用的是numbers而不是用number?

kiwifoodtown

请仔细读句子，数目不断下降，是指由多个数字相比较而且是个不断变化的过程，而不是简单的由单一一个数字同以前的一个数字的比较，所以这里用numbers。