在非限制性定语从句中,as和which可代替整个句子.这句话怎么理解?

Question

同上

Answer 1

as, which 非限定性定语从句

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。例如：

As we know, smoking is harmful to one's health. 如我们所知，吸烟有害健康。

The sun heats the earth, which is very important to us. 太阳使地球暖起来，这对我们人类很重要。

典型例题

1）Alice 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。

2）The 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。

3）It 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……。例如：

I have got into the same trouble as he （has）. 我碰到了跟他一样的麻烦。

例2. as可引导非限制性从句，常带有'正如'。例如：

As we know, smoking is harmful to one's health. 如我们所知，吸烟有害健康。

As is known, 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。

Answer 2

在非限制性定语从句中， which代替前面整个句子
而不具体指某一个东西
但His naughty grandson has taken away his glasses,_\without\
which the old man can see nothing .

which代替前面整个句子
而不具体指某一个东西
——这只是一个方面，是特例，而修饰先行词才是它的普遍用法，所以此句子which 便指代glasses ，很正常

两者区别主要有两点
(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.

which 在非限制性定语从句中，作为关系代词，可以做定语和表语。例如：
We told him to consult the doctor, which advice he took.(which在从句中做定语，修饰名词advice).

The two policemen were completely trusted, which in fact, they were.(which在此做表语）

As 在非限制性定语从句中，可做关系代词。
例如：

The two brothers were satisfied with this decision,as was agreed beforehand.
(as 在此做关系代词，它的先行词是this decision
在从句中做主语）