____we must do is___the use of energy.B.What ;t

B
其实C 也是对的.
不定式作表语时一般不可以省去to,但：
当主语部分有do,作“做”讲,表语陈述做的事时,不定式符号to 可以省去,也可以不省
如：
The first thing that you shoud do is (to) improve your English.
What you should do is (to) help them out
The first thing for you to do is (to) find out when the train leaves.
请在客户端右上角评价点“满意”即可哇塞，不是吧，又是你~ ^_^就是说C也对咯？哇塞， 不愿看到我呀？是的愿意啊，，，那这道题可不可以从must 后面加do的角度解释？就是那个do喔喔~谢啦