关于prep12pack1-sc-064的问题

Althoughbeavers canstill be found throughout the western United States, their number has declined  compared with the eighteenth century, when the abundance of beaverslured armies of European trappersinto the Rocky Mountainregion to slaughter them for their pelts.

A.         their number has declinedcompared with

B.          their numbers have compared with

C.         their numbers have declinedsince

D.         their numbers have in comparison to those of

E.          the number of them declinedsince