受格的关系代名词可省略
The sandwiches (which) we ate for lunch were not delicious.
Soccer is sport I like (the)best.
The covers I have are my bed are heavy.
介系词+受格关系代名词
The man who/whom/that you are speaking of is our principal.
The man you are speaking of is our principal.
The man of whom you are speaking is our pincipal.
The train which/that we are waiting for is now half an hour late.
The train we are waiting for is now half an hour late.
The train for which we are waiting is now half an hour late.
介系词放关系代名词前, 关代不可用that, 也不可省略
关系代名词只用that
先行词前有最高级
Today is the coldest day (that) we have experienced.
先行词前有序数
Kenny was the first boy that rushed out of the classroom.
先行词为人、事物或动物同时出现
Take a look at the boy and his dog that are coming this way.
先行词前有疑问词who(谁)、which(哪一个
who that has seen the photos of starving children doesn't want to help them?
which was the bag (that) you left in the train?
先行词有all, no, every, any, ……thing, ……one
All (that) students have to do is (to)study hard.
what students have to do is (to)study hard.这里的what=all+that
She has every thing (that) a woman could wish for.
先行词前有the only, the same, the very(正是)
He was the only one that trusted me.
This is the very novel that I have looked for.
※口诀：
1. 最高级、序数、人+物、避免重复。
2. all, no, every, any, the……
限定用法及非限定用法
限定用法
He has two daughters who became actresses.女儿可能不只两个
非限定用法
He has two daughters,who became actresses.女儿只有两个
I,who is your best friend,centainly will help you.
My brother,who is dentist,is studying in the US.
