[观察例句]
1．I walk through the doors into the waiting area，where there's a familiar atmosphere of boredom and tension.
2．People sit uncomfortably on plastic chairs，looking through old magazines，all of which have been read hundreds of times previously.
3．In the middle of this particular scene I spot a small girl whose ankle is twice its normal size.
4．I speak with the onduty nurse，who tells me that Lara's parents rushed her to the hospital...
5．Scientific studies show that laughter produces chemicals to make people feel better，which means clown doctors can be helpful.
[归纳用法]
一、限制性定语从句与非限制性定语从句概述
1．限制性定语从句通常紧跟在先行词之后，对先行词起限制确定作用。从句和先行词的关系十分密切，两者之间一般不可用逗号隔开。
She has found the necklace (that) she lost two weeks ago.
她找到了那条两周前丢失的项链。
2．非限制性定语从句是对先行词的一个补充说明。没有它，主句也能独立存在；非限制性定语从句和先行词的关系不是很密切，两者之间用逗号隔开。
He has two sisters，who are working in the city.
他有两个姐姐，她们在城里工作。
