定语从句which的用法是什么
定语从句which的用法
which是定语从句的关系代词之一。GMAT语法考试限定，which有且仅有两种用法。
一，which前面有逗号，逗号前面是个名词，which就近指代那个名词。
(1) Tankfield emailed Pea some photos, which did not cheer Pea up.
which就近指代photos，定语从句中谓语动词did not cheer (Pea up)的发出者即从句主语即先行词photos，是photos没让豌豆家属高兴起来。
(2) Tankfield emailed Pea some photos, which Pea did not find interesting.
which就近指代photos，photos是定语从句中的宾语，把定语从句还原成一个完整句就是Pea did not find the photos interesting.
可以看到，上面两个句子都可以以that为关系代词改写，即
(1)’ Tankfield emailed Pea some photos that did not cheer Pea up.
(2)’ Tankfield emailed Pea some photos that Pea did not find interesting.
改写与原版区别在哪儿?就在一个逗号。which前面是名词，名词和which之间没逗号的，在GMAT语法里算错。
二，which前面是介词，介词前面是名词，which就近指代介词前的那个名词，名词和介词之间有无逗号均可。
Tankfield once lent Pea a book from which Pea glimpsed the basics of genes.
这个句子可以“拆”成如下两句：(每个定语从句都可以拆成两句，以先行词为拆分点)
Tankfield once lent Pea a book. Pea glimpsed the basics of genes from the book.
先行词实际上是定语从句中介词的宾语，这时，需要把介词提前，避免如下表达：
Tankfield once lent Pea a book, which Pea glimpsed the basics of genes from. (XXX)
Tankfield once lent Pea a book that Pea glimpsed the basics of genes from. (XXX)
上中学的时候学过，which引导的定语从句叫“非限制性定语从句”，是不是?它怎么就“非限制性”了?回顾上述GMAT语法规定which有且仅有的两种用法，which指的都是就近的名词，从句其实还是限制性的.。
所谓非限制性呢，是说which指逗号之前一套主谓所描述的情况，以逗号前的一个完整句为先行词。比如：
Tankfield might never care to say Happy Birthday to Pea, which was rather sad.
Tankfield might never care to say Happy Birthday to Pea, which Pea did not refuse to acknowledge to herself any more.
注意事项：
这样的非限制性定语从句在GMAT语法中是不成立的，关于which，GMAT语法考试只认可上述两种限制性用法。那么，在GMAT语法考试规则范围内，用什么方法能够表达出原来学过的非限制性定语从句的意思来呢?
分成两句或做出同位语来都是可以的，当然，需要先找出一个名词把原来非限制性定语从句的先行词(即那个完整的句子)概括出来。
一、分成两句
Tankfield might never care to say Happy Birthday to Pea. The fact was rather sad.
Tankfield might never care to say Happy Birthday to Pea. Pea did not refuse to acknowledge the fact to herself any more.
二、做同位语
Tankfield might never care to say Happy Birthday to Pea, the fact, rather sad, being what Pea did not refuse to acknowledge to herself any more.
