一、that: 可指人或物;在定语从句中作主语，宾语，表语。(指人时，相当于who或 whom;指物时，相当于which)(一般不用于非限制性定语从句; 不可置于介词后作宾语) 如：
1. A letter that/which is written in pencil is difficult to read. (主语)
2. Do you know the gentleman that/who spoke just now?
3. You can take anything ( that) you like. (宾语)
4. What is the question (that/which) they are talking about?
5. Here is the man ( who/whom/that ) you want to see.
6. She's no longer the girl ( that) she used to be before.(表语)