关系代词只能用that的几种情况(for Junior 3)引导定语从句的关系代词that和which，在一般情况下，不管关系代词在从句中作主语或宾语都可替换使用。例如： He bought a mobile phone thatwhich looks like a lighter（作主语）他买了一个样子像打火机的手机。 Ive found the book thatwhich he lost three days ago（作宾语）我找到了他三天前丢的那本书。 但在下面几种情况下，引导定语从句的关系代词只能用that，而不用which： 1先行词是复合不定代词everything，anything，nothing等时。例如： She didnt forget anything that her mother had told her to buy她没忘记妈妈让她买的任何东西。 注意：先行词是something时，关系代词用that或which都可以。例如： I want to buy something that which the old men like to eat我想买点老人喜欢吃的东西。 2先行词被序数词或the last修饰时。例如： This is the first textbook that I studied in the primary school这是我在小学学的第一本教科书。 He is in the last row that is next to the window他在挨着窗户的最后一排。 3先行词被形容词最高级修饰时。例如： That is the highest building that I have seen那是我见到过的最高的大楼。 Have you worked out the most difficult maths problem that our teacher told us to do？你解出老师让我们做的那道最难的数学题了吗？ 4先行词是或被all，no，some，any，little，much等修饰时。例如： Ive written down all that（ what）the teacher doesnt allow us to do我已记下了老师不允许我们做的一切事情。 They havent got any dictionaries that we need他们没有我们所需要的任何字典。 5先行词被the only，the very，the same等修饰时。例如： This is the very novel that you want to borrow这就是你想借的那本小说。 注意：先行词被the same修饰时，关系代词也可用as。例如： I need the same dictionary thatas you have我需要同你的一样的字典。 关于as的用法，我们以后在高中阶段还会学到。 6先行词是两个或多个分别表示人和物的名词时。例如： He told us many interesting things and persons that we had never heard他给我们讲了我们从没听到过的人和事。 7主句是以who，which引导的特殊疑问句时。例如： Who is the man that you spoke to just now？你刚才跟他说话的那个人是谁？ Which is the book that you want to borrow？你想要借的书是哪一本？ 8先行词是主句的表语或关系代词在定语从句中作表语时。例如： China is no longer the country that it used to be中国再不是以前那样的国家了。