is known to us all he is an excellent student in our class.A. WhoB. ThatC. WhichD. As

问题补充：

is known to us all, he is an excellent student in our class.

A. Who

B. That

C. Which

D. As

答案：

A. Who

B. That

C. Which

(答案→)D. As

解析：句意：我们都知道，他是我们班一个优秀的学生。这里用as引导定语从句，在定语从句中as做主语，而且修饰后面的主句内容，意思是“正如”，所以选D。