在定语从句中，关系代词which和that都可以指物，一般情况下可以互换使用。但在下列情况下要特别注意，区别如下：

1. 只能用that的情况：

（1）当先行词为不定代词: all，little, few, much, none, something, anything ----

There's nothing that will stop us making progress. 没有事情会阻止我们进步。

（2）当先行词被下列词修饰时: only, the last, the very----

This is the only that Tom can't work out. 这是Tom唯一不能解决的问题。

（3）当先行词为: 序数词或被序数词修饰时。

She was the first woman that climbed the Qomolangma.

她是第一个登上珠穆朗玛峰的妇女。

（4）当先行词为: 同时包括人和物时。

I still remember the college and the teacher that I visited in London years ago.

我还记得几年前在伦敦参观的大学及拜访的老师。

（5）当先行词被: 形容词的最高级修饰时。

The Great Wall is the best place that I have ever visited.

长城是我参观过的最好的地方。

（6）当先行词在定语从句中作表语

He is no longer a little boy that he used to be.他不再是过去的那个小男孩了

（7）当主语是以who或which开头的特殊疑问句时。

Which is the film that you saw yesterday？你昨天看的是哪一部电影？

2. 只能用which而不能用that的情况

（1）关系代词前面有介词。

The room in which Lucy lives is very clean and tidy. 露西住的房间干净整洁。

（2）先行词本身是代词that或those 时。

He doesn't take that which is expensive.他不要太贵的那一个。

注意：

当关系代词在从句中作主语时，从句中的谓语动词要与先行词的单复数形式保持一致。

例如：

（1）I prefer movies which give me something to think about.我更喜欢令我深思的电影。

（2）I love the teacher who is friendly to the students.我喜欢对学生友好的老师。

口诀记忆：