which→在定语从句中做主语或宾语→用来指物
① 这是你想要的那本书。This is the book which youwant.
② 我喜欢红色的那辆车。I like the car which is red.
③河边的那幢楼是我们的学校。The building which stands near the river is our school .
必须用which的4种情况：
(1) 当关系代词前面有介词时 Thisis the house in which he once lived .
(2) 引导非限定性定语从句
(3) 一个句子中有两个定语从句，为了避免重复，一个用which一个用that
He bought an American magazine that could give him so much Englishknowledge and which could help him
to kill time .
(4) 当先行词本身是that时 Theclock is that which tells the time .
5 that→在定语从句中做主语或宾语→用来指人或指物（可以用who, whom, which替换）
必须用that的9种情况：
⑴ 先行词是all, everything, nothing, few, little, much , something ,anything , none等不定代词时，必须用that引导。
我会告诉你我知道的一切。I shall tell you everythingthat I know.
有什么我能为你效劳的吗？ Is there anything that Ican do for you ?
⑵ 当先行词被序数词或形容词最高级修饰时必须用that引导。
我不会忘记我学过的第一课。I can’t ∕ won’t forget thefirst lesson that I learned.
② 他是我见过的最可恨的人。He is the mosthateful person that I’ve seen.
⑶当先行词被all, every, little, few, no等修饰时，必须用that引导。
① 有常识的人都不会相信的。No man that hascommon sense can believe it .
② 我喜欢你给我的所有的书。I like all the books that you gave me.
⑷当先行词被the only（唯一的）；the very（恰好，正好）；the same（相同的）；the last(最后的)等修饰时，必须
用that引导。
① 你是我唯一喜欢的人。You’re the only person thatI like.
② 这就是我正想买的那本书。This is the very book that I want to buy .
⑸当先行词既有人又有物时，必须用that引导。
我不知道他们正在谈论的人和事。 I don’t know those persons and things thatthey are talking about.
火车朝正在过铁轨的那个男孩和他的狗驶去。
The train ran over to the boy and his dog that were just crossing thetrack .
⑹当that用做关系副词，修饰表示时间的名词时，可以代替when来引导。
我不会忘记我第一次见到你的那一天。I can’t forgetthe day that ∕ when I first met you.
事情发生在我出生的那天。 It happened on the day that/ when I was born .
⑺当句子中已有who或which出现时，必须用that引导。
① 正在唱歌的那个女孩是谁？ Who is the girl that is singing?
② 哪个是他昨晚待过的酒店？Which is thehotel that he stayed at last night ?
（8）当先行词是“to be ”后面的表语，或者关系代词本身在从句中作表语时
① The school isquite different from the one that it used to be .
② He isn’tthe man that he was .
（9）当主句以here , there 开头时
① Here is the hotelthat you’ve been looking for .
② There is aseat in the corner that isn’t taken .
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