【题目】She brought with her three friends, none of ________ I had ever met before.
A.them
B.who
C.whom
D.these

【答案】C
【解析】句意：她同来的有三个朋友，以前我都没见过这些人。分析句子结构可看出，“none of ________ I had ever met before”是非限制性定语从句，修饰three friends。of是介词，之后要用表示人的关系代词whom。所以答案是C。