2012届高考英语语法专题复习定语从句特例。
引导非限制性定语从句，当先行词是一个单词或词组时，我们只用which引导，不用as引导。例如：
1、beijing, which will hold the 2008 olympic games, is becoming more and more beautiful.
但当代替的是主句的全部内容时，区别如下：
一，as引导的非限制性从句可置于主句之前，之中或之后，而which引导的非限制性定语从句只能放在主句之后。例如：
1，as we know, the earth goes around the sun.
2, the earth goes around the sun., as we know.
3,the earth, as we know, goes around the sun .
4, the earth goes around the sun, which makes us get enough sunlight.
二，as引导的从句有“正如…… 正像…… 之意，而which引导的从句则没有此意，因此，当主从句语意一致时，只用as引导，不用which引导。常用句式有：as anybody can see, as we expected, as we know, as is often the case, as we hoped，as often happens 等例如：
1,he is a kind man, as has been said above .
2,she has married again, as was expected.
3, she has married again, which was unexpected .
三，as作从句主语，而且从句为被动语态，此时不用which引导；若从句为主动语态，一般用which引导。例如：
1，their team won the game again , as was reported.
2,tom has made great progress, which delighted us .
as作此种用法时，常用的句式有：as is known to us all, as is said above, as is announced,as was reported, as is mentioned above ,as is reported, as is expected, as is discussed 等。
四，which引导的非限制性定语从句指代整个主句内容时，从句的谓语带有宾语，有的还带有宾语补足语。此时which无词义，只是代表主句的意思，可以译为"这件事","这一点";而as可以译为"正如……"例如下面这些句子中的which就不能替换为as 。
1，i shall never forget those years when i lived in the country with the farmers, which has a great effect on my life.
2, bamboo is hollow, which makes it very light .
made rapid progress at school, aswhich pleased his parents a lot .×
五，as引导的非限制性定语从句常表示主动，而which引导的非限制性定语从句常表示被动。例如：
1，he says he has a lot of money, which isnt true .
2, he has a lot of money, as he says .
另外as引导限制性定语从句时，主要与the same, such等连用。例如：
1，let children read such books as will make them better and wiser.让孩子们读那些能使变得更好更聪明的书。
2, this is the same book as was bought in the bookstore yesterday.
as与such结合引导限制性定语从句时，要注意和such……that……引导的结果状语从句区分开。例如：
1，he gets such a good book as we all want to read first.
2, he gets such a good book that we all want to read it first .
such things __can be proved can be regarde as facts .
在第一句中，as作为read的宾语，as引导的是定语从句，而在第二句中，that引导的是结果状语从句，read必须跟it宾语；而在第三句中指代事物的先行词前虽然有only， 但此处only并不是直接修饰things，而且也不是“唯一”的意思。此题考察固定结构such…as，故空格处应该填上as 。
作为高中生，掌握了as和which这些基本用法，并加以适当的练习，定能以不变应万变了。
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