1定语从句悉升中的先行词还原到从句中，看先行词充当什么启森成分，若充当状语，则when\where\介词+which三种关系副词。
2若介词放在关系代词前，关系代词指人时用whom，不可用who或者that；指物时用which，悄陆亩不能用that；关系代词是所有格时用whose
(1) The man with whom you talked is my friend. .
(2) I bought many books yesterday, three of which are written by Lu Xun.
比如：The man to whom I refer is a teacher.
