英语单项选择（最好有详细解释）
6. He is a man of great knowledge,___ much can be learned.
A. in whomB. about whomC. from whomD. of whom
7. Do you know the man___ just now?
A. to who I nodded B. I nodded to
C. whom I nodded D. whom I nodded to him
8. The man___ has gone to Japan.
A. whom I told you B. that I told you
C. whom I told you about him D. I told you about