很多同学可能都会觉得在使用定语从句的时候，有时不知该选择that还是which作为引导词。其实只要记得以下几点，并多做练习，在具体的句子中加以理解，一切问题就可以迎刃而解了。
首先，that和which在从句里都可以做宾语和主语，做宾语时可以省略。在定语从句中,有种说法叫"关宾省",意思是关系代词在限制性定语从句中作宾语可以省略,不管是that，which，还是whom。但是which能引导非限制性定语从句，that则不行。

其次，记得以下只能用that的几种情况：
1. 当先行词为all, much, little, none及由any, every, some, no所构成的复合不定代词时。
如：We should do all that is useful to the people. 我们应该做一切有益于人民的事情。
Please tell me anything that you know about the matter. 有关此事，凡是你所知道的请告诉我。

2. 当先行词被any, few, little, no, all, much, some等词修饰时。
如：You can take any seat that is free. 任何空着的座位你都可以坐。
There is little work that is fit for you. 几乎没有适合你的工作。

3. 当先行词为序数词或被序数词所修饰时。
如：When people talk about the cities of China, the first that comes to my mind is Beijing. 人们谈论起中国的城市的时候，我首先 想到的是北京。
This is the fourth film that has been shown in our school this term. 这是我们校本学期放映的第四部电影。

4. 当先行词为形容词最高级或被形容词最高级修饰时。
如：The best that I could do was to apologize. 我唯一能做的就是赔礼道歉了。
This is the most interesting story book that I have ever read. 这是我读过的一本最有趣的故事书。

5. 当先行词被the very, the only, the last, the just, the same等修饰时。
如： This is the very book that I’m looking for. 这正是我在找的书。
The only thing that we could do was to wait. 我们唯一能做的事就是等待。

注意：先行词被the same修饰时，关系代词也可用as。
如：I need the same book that / as you have. 我需要有你一样的书。

6. 当先行词既包含人又包含物时。
如： They are talking of the heroines and their deeds that interest them. 他们正在谈论他们感兴趣的女英雄及她们的事迹。

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