is known to everybody that the moon travels round the earth.A. ItB. AsC. WhenD. Where

问题补充：

is known to everybody that the moon travels round the earth.

A. It

B. As

C. When

D. Where

答案：

(答案→)A. It

B. As

C. When

D. Where

解析：考察it作为形式主语。本句中的It是形式主语，真正的主语是后面的that the moon travels round the earth。这里的that只是一个引导词而已，不在句中充当任何成分。句意：众所周知的事情是月球绕着地球转。故A正确。