介词选择要根据从句的动词来定
eg:I don't know the person with whom you talked just now.我不认识刚才和你讲话的人.此处从句为 talk with sb.和某人交谈.用talk with
I don't know the person about whom you talked just now.我不认识你刚才谈论到的那个人.此句中为talk about sb.谈论某人.用talk about
当先行词是物的时候用which是,也是考虑从句动词与先行词的搭配
eg.could you find the bus by which you get here.
could you find the bus in/on which you saw the fight.