Question

________ has been mentioned above, the government is focusing on constructing(建设)a harmonious society．

1. A.
   As
2. B.
   That
3. C.
   What
4. D.
   Which

Answer 1

A
解析：考查非限制性定语从句，as引导非限制性定语从句时可以放在句首，which引导的非限制性定语从句一般不置于句首。
讲台挥洒一刻：
as引导的定语从句与which引导的非限制性定语从句的区别
1)as引导的非限制性定语从句，既可在主句前，又可在主句后，有时还可插入主句中，而which引导的非限制性定语从句只能置于主句之后；as有“正如/像……一样”之意。而which没有。相同的是两者都可替代主句的整个内容，而不是主句中的某一个词。例如：
The weather turned out to be very good, which was more than we could expect．
2)当非限制性定语从句放在主句前面时，只能用as。
例如：
As is known to everybody, the moon travels round the earth once every month．
＝The moon travels round the earth once every month, as/which is known to everybody．
＝It is known to everybody that the moon travels round the earth once every month．
＝What is known to everybody is that the moon travels round the earth once every month．
后两句属名词性从句范畴。
3)当定语从句放在主句后面时，也并不是as就永远等于which。
(1)当定语从句是否定句或表示否定时只能用which。例如：
He came here very late, which was unexpected(not expected)．
Mr．Smith usually praises his student Rose in public, which she doesn't like at all．
(2)当as在从句中作主语时，后面常接动词的被动语态。例如：
be known, be said, be reported, be announced等。如果从句中行为动词是主动语态，一般用which作主语。
例如：
She has been absent again, as is expected．
她又缺席了，这在预料之中。
Tom has made rapid progress, which makes me very happy．汤姆取得了很大进步，这使我很高兴。
4)as多用于下列习惯用语中：as anybody can see正如人人都能看到的那样；as is well known＝as is known to all众所周知；as we had expected正如我们所预料的那样；as often happens正如经常发生的那样；as has been said before如上所述；as is mentioned above正如上面提到的。