that引导的定语从句不能用在介词后面。如果介词后面跟定语从句，要用which而不能用that.
例句：
This is the house(that/which/省略) Tom lived in many years ago.
此句是定语从句，先行词是house,关系代词在从句中去宾语，因介词在从句的谓语动词的后面，所以可以用that引导，也可以which用引导,也可以省略。但是要把介词提前，只能用which引导而不能用that引导。即：
This is the house in which Tom lived many years ago.
