1.做定语,如：The book in which the pictures are black and white is mine.
主句是：The book is mine.
定从是：The pictures are black and white.
在复合句中in chich作定语.
2.作状语,如：The boy with whom I will go to your home is my best friend.
主句是：The boy is my best friend.
定从是：I will go to your home with him.
在复合句中with whom作状语.