Question

I sent invitations to 90 people, ________ have replied.

1. A.
   of whom only 30 of them
2. B.
   of whom only 30
3. C.
   only 30 of those who
4. D.
   only 30 who

Answer 1

B
名词/代词+of+关系代词(which/whom)常引导非限制性定语从句，of whom only 30＝only 30 of whom．