is known to everybody the moon travels round the earth once every month.A. It B. AsC. T

问题补充：

is known to everybody, the moon travels round the earth once every month.

A. It

B. As

C. That

D. What

答案：

A. It

(答案→)B. As

C. That

D. What

解析：as 引导的是一个非限制性定语从句。