The girl with_____they are playing is 13 years old

题目

The girl with_____they are playing is 13 years old
A.that B.who C.whom
这道题还原应该是they are playing with 所以应该选C
可是with是介词 空里不应该填"which"吗

答案

The girl is 13 years old.
with whom they are playing.
就是they are playing with whom,whom 是指代the girl 介词后面嘛