老师讲到that引导定语从句作介词宾语时,介词不可提到that前,介词后需用which或whom代替是什么意思?

题目

老师讲到that引导定语从句作介词宾语时,介词不可提到that前,介词后需用which或whom代替是什么意思?
并举例说明,

答案

如果定语从句中出现把从句中的介词提前到关系代词which和whom之前,这时候关系代词which和whom 作介词宾语时,关系代词不能省,介词提前关系词不能用that .比如： This is the pen ( which /that) he wrote his compo...