1. 引导限制性定语从句和非限制性定语从句
(1)as多与such 或the same连用,可以代替先行词是人或物的名词。
(2)as 也可单独使用,引导非限制性定语从句,作用相当于which。例如:
The elephant’s nose is like a snake, as anybody can see.
(3)the same… that与 the same …as在意思上是不同的。
2.As引导的非限制性定语从句的位置
as引导的非限制性定语从句位置较灵活,可以位于主句前面.中间或后面,一般用逗号与主句隔开,但which所引导的非限制性定语从句只能放在主句之后。例如:
(1) As is expected, the England team won the football match.
(2) The earth runs around the sun, as is known by everyone.
as引导非限制性定语从句既可放在主句之前,也可放在主句之后,用来修饰整个句子。通常用下列句型:as is known to all, as is said, as is reported, as is announced, as we all know, as I expect 等。
e.g. As I expected, he got the first place again in this mid-term examination. 正如我所预料的那样,他在这次期中考试中又获得了第一名。
as 引导非限制性定语从句时与which的区别
①当主句和从句语义一致时,用as;反之,用which来引导非限制性定语从句。
e.g. He made a long speech, as we expected.
He made a long speech, which was unexpected.
②当非限制定语从句为否定时,常用which引导。
e.g. Tom drinks a lot every day, which his wife doesn’t like at all.
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