问题补充:
is mentioned above that the number of the students in senior high school is increasing.
A. Which
B. It
C. That
D. As
答案:
A. Which
(答案→)B. It
C. That
D. As
解析:考查it做形式主语:句意:上面提到的是高中的学生数量在增加。It是形式主语,that引导的是主语从句,which和as应该引导非限制性定语从句,that引导的是主语从句,选B。