We are taking action but how effective it will remain .A. to seeB. to be seenC. seeingD.

问题补充：

We are taking action, but how effective it will remain .

A. to see

B. to be seen

C. seeing

D. seen

答案：

A. to see

(答案→)B. to be seen

C. seeing

D. seen

解析：考查remain的用法，remain to be done“仍然要被做”，句意是：我们正在采取行动，但是它的效果如何还有待证实。选B