In the cafeteria I saw my sister and her three friends none of I had ever seen before.A

问题补充：

In the cafeteria, I saw my sister and her three friends, none of I had ever seen before.

A. them

B. which

C. whom

D. those

答案：

A. them

B. which

(答案→)C. whom

D. those

解析：考察定语从句。本题定语从句的先行词是my sister and her three friends，关系代词whom指代先行词my sister and her three friends作为介词of的宾语。因为先行词是人，且作为宾语，故使用whom。AD两项不能引导定语从句，which的先行词是物。故C正确。