这两个关系代词引导定语从句时，都可以指物，在从句中都可作主语或宾语，作宾语时都可省略。例如:
The train that (which) has just left is for Shanghal. (作主语)
刚开的那列火车是去上海的。
The film that( which) we saw last night is wonderful. (作宾语，可省略)
我们昨天晚上看的电影好极了。
二、不同点〈一〉以下情况常用that,一般不which。1.当先行词基不定代词或被它们修饰时，例如:Is there anything that I can do for you?
有什么要我做的事吗?
All that can be done must be done.
凡能做的事情都必须做。
He answered few questions that the teacher asked.
他几乎没有回答老师的那些问题。
2.当先行词被形容词最高级或序数词修饰时。例如:This was one of the most interesting books that were sold in this bookstore.
这是这家书店售出的最有趣的书之一。
The first thing that should be done is to get some food.
该做的第一件事是弄点吃的。
3. 当先行词有the very , the only, the same等修饰时。例如:That's the only thing that we can do now.
目前我们只能这样了。
Those are the very words that he used.
那就是他的原话。
4. 当先行词是一个既指人又指物的并列词组时。例如:They were talking about the persons and things that they saw in the factory.
他们在谈论在工厂里看到的人和事。
5. 当关系代词在定语从句中作表语时。例如:China is not the country that it was.
中国已经不是过去的中国了。
6. 当要避免与疑问词which重复时。例如:Which is the car that was made in Bejjing?
哪辆车是北京制造的?
〈二〉以下情况用which,不用that1.引导非限制性定语从句。例如:Footbll, which is an nteresting game, is played all over the world.
全世界都踢足球,它是一项有趣的运动。
2.直接放在介词后作宾语时。例如:Ianguage is the most important tool without which people can't communicate with each other.
语言是最重要的工具。没有它，人们便无法交流。
that; 和which的区别,很容易记混,用下面的顺口溜便不难区分: that,which可互换，下列情况勿照办:that情况比较多，不妨对你说一说;
不定代词这路货，全用that准没错。
先行词前被限制，千万不要用which，
要用which别着急，介词提前逗隔离。
