英语什么情况下只能使用AS引导的从句.比如这道题：（ ）is mentioned above,the number of the students in senior school is increasing.A.Which B.As C.That D.It 我的老师说通过句子成分分析,这道题就只能选择B.As,为什么这么肯定,究竟是怎么判断出来的?又是如何判断出来是定语从句的呢?
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which不能做主语?
这类题常考的.
首先你要明了这是个定语从句.
其次,这是从句在前,主句在后.定语从句的先行词是主句一整个句子.
当先行词是主句一整个句子的时候,这个定语从句只能用Which或As来引导,但是,Which引导的从句只能放在主句的后面.排除了A.D是个代词不是连词,排除.
你再领会下这几个句子,全是对的：
As is mentioned above,the number of the students in senior school is increasing.
The number of the students in senior school is increasing, which/ as is mentioned above.
这两个是定语从句
It is mentioned above that the number of the students in senior school is increasing
这是IT作形式主语,THAT引导的主语从句放在了后面.
What is mentioned above is that the number of the students in senior school is increasing
这是主语从句+IS系动词+表语从句
考试时,这几个句型常拿来考查.