Question

Susan invited some friends, ________ were girls.

1. A.
   three of them
2. B.
   three
3. C.
   they
4. D.
   three of whom

Answer 1

D
解题思路：这是一个非限定性定语从句，先行词是人，关联词是who，whom，that．that不能引导非限定性定语从句，who在从句作主语；whom作宾语，还可以作介词宾语，如本题．