(1)關系代詞在定語從句中作賓語 She is the girl (whom / that) I loved before. (可以省略whom/that)(2)關系代詞在定語從句中作表語He is no longer the boy (that) he used to be. (可以省略that)(3)關系代詞作介詞賓語，介詞在從句句尾時可以省略Housing price is a problem (that/which) people are interested in.比較：Housing price is a problem in which people are interested.（此時只能用which且不能省略）
