I 定语从句
1. 先行词为all, anything, something, nothing, everything, much, little, none等不定代词时，关系代词一般只用that，不用which。在大多数情况下that可以省略.
Please tell me everything you know about the matter.
Thats all we can do at the moment.
2. as引出的限制性定语从句
在such as的.结构中as可作关系代词，引出限制性定语从句。有时和same连用，在从句中可作主语、宾语或表语等。
Such people as were recommended by him were reliable.
Ive never seen such a talented young man as he is.
I have the same trouble as you .
3. as引出的非限制性定语从句
as可作关系代词引出非限制性定语从句，代替整个主句，通常译为如一样，象一样等。as引导的从句一般用逗号与主句隔开，可以位于主句的前面、中间或后面.
I live a long way from work, as you know.
She did not, as her friend had feared, break down.
As is generally accepted, economic growth is determined by the smooth development of production.
4. 分隔式定语从句
定语从句一般紧跟在先行词之后，但有时会被其他句子成分与先行词隔开，从而构成分隔式定语从句。
