山东自考本科00015英语二考试必考考点：定语从句（七）

关系代词as也可引导非限制性定语从句，其从句的谓语常是表示感知的动词，如：know, see, hear, expect等。从句可放在主句之前、之中、或之后。As可以指主句中的某个成分，也可以指整个主句，as在从句中可以作主语、宾语或表语。例如：

1）    Tom, as you know, is a writer.

2）     As we have seen, oceans cover more than 70% of the earth.

3）     Tom doesn’t find his homework, as often happens.

4）     Charlie looks strong, as in fact he is.

由as, which 引导的非限定性定语从句，as和which可代整个主句，相当于and this或and that。As一般放在句首，which在句中。

As we know, smoking is harmful to one's health.

The sun heats the earth, which is very important to us.     

典型例题   

1Alice received an invitation from her boss, ___came as a surprise.

A. it   B. that   C. which    D. he

答案C. 此为非限定性从句，不能用 that修饰，而用which，it 和he 都使后句成为句子，两个独立的句子不能单以逗号连接。况且选he句意不通。

2The weather turned out to be very good, ___ was more than we could expect.  

A. what  B. which  C. that  D. it

答案B。which可代替句子，用于非限定性定语从句，而what不可。That 不能用于非限定性定语从句，it不为连词，使由逗号连接的两个句子并在一起在英语语法上行不通。

3It rained hard yesterday, ____ prevented me from going to the park..

A. that  B. which    C. as   D. it

答案B.  

as 和which在引导非限制性定语从句时，这两个关系代词都指主句所表达的整个意思，且在定语从句中都可以作主语和宾语。但不同之处主要有两点：

(1） as 引导的定语从句可置于句首，而which不可。

(2） as 代表前面的整个主句并在从句中作主语时，从句中的谓语必须是系动词；若为行为动词，则从句中的关系代词只能用which。

在本题中，prevent由于是行为动词，所以正确选项应为B。

As 的用法

例1. the same… as；such…as 中的as 是一种固定结构, 和……一样……。

I have got into the same trouble as he (has).

例2. as可引导非限制性从句，常带有'正如'。

As we know, smoking is harmful to one's health.

As is know, smoking is harmful to one's health.

As是关系代词。例1中的as作know的宾语；例2中，它充当从句的主语，谓语动词know要用被动式。