which和that是英语中常用的从属连词，即，关系代词。它们在定语从句中可以做主语、宾语及介词的宾语等。除此之外，它们在用法上有一些差别，而且这些不同会经常出现在考试中。
1.which和that在定语从句中作主语
The river, which flows through our village, is called Shahe River.流经我们村的那条河被称为沙河。The lioness rejected the smallest cub, which died.母狮排斥最小的幼狮，把它饿死了。
He became more aware of the things that started the tension off.他对造成那些紧张气氛的因素更加清楚了。
2. which和that在定语从句中作宾语
I got the magazines which/that my daughter sent me yesterday.我昨天收到了女儿邮寄的杂志。This is the book that/which you wanted.这就是你要的书。
3. which和that在定语从句中作介词宾语
This is a subject about which we might argue for a long while.这是一个我们要争论很久的题目。关系代词指物，作介词宾语时，只能用which，不能用that。
要点及考点：
1.当从句主语指人时，可以用that，但who用得更多一些。但是，在定语从句中最高级的处，that用得多于who。比如：
Who do you think was one of the greatest scientists that ever lived?你认为谁是世界上最伟大的科学家之一？
2.在限定性定语从句中，如果关系代词which或者that作宾语，则常被省略。比如：
It is a language point (which) the students must master.这是学生必须掌握的一个语言点。 He did not get the letter (that) you sent him.你给他的信他没收到。
3.如果关系代词前面紧邻介词，那么不能省略关系代词，而且不能用that，只能用which。比如：
The day on which I met him was the greatest of my life.我遇到他的那一天是一生中最美妙的一天。
3.在非限定性定语从句中，只能用关系代词who，whom代表人，用关系代词which代表事物。比如：
I met my classmate, who is a teacher now.我遇到了我的同学，他现在是老师。
He was a great and valued personal friend whom I've known for many years.他是个非常好的、很宝贵的私人朋友，我们已相识多年。
4.有时which不是代表一个名词，而是代表前面的整个句子或者它的一部分意思。比如：
Tom drove too fast, which was reckless.汤姆开车太快，这太鲁莽了。
He invited us to dinner, which was very kind of him.他邀请我们共进晚餐，真是太好了。He said he had never seen her before, which was untrue.他说他从未见过她，这是不真的。