is mentioned(提及) above the number of the students in senior high schools is increasing.A

问题补充：

is mentioned(提及) above, the number of the students in senior high

schools is increasing.

A. Which

B. It

C. What

D. As

答案：

A. Which

B. It

C. What

(答案→)D. As

解析：考查非限制性定语从句。排除B，C;且在句中有正如，正像之意，所以选D，句意：正如上面所提到的。高中学生的数量正在增加。