定语从句常用引导词有：that, which, who, whom, whose, as, where, when, why
1．that 可以指人或物，在从句中作主语或宾语 (作宾语可省略)
I like the books that were written by Lu Xun.
The student that won the first prize is our monitor.
2．which 指物，在从句中作主语或宾语 (作宾语可省略)
These are the trees which were planted last year.
Is this the library (which) you borrow books from?
3．who指人，在从句作主语或宾语 (作宾语可省略)
……
