once ----,this power station will supply all the neighboring towns and villages with electricity.

题目

once ----,this power station will supply all the neighboring towns and villages with electricity.
A.it being completed B,it completed C.it was completed D.it completing
为什么选B而不选A呢?

答案

being completed指某事物正在被完成.
completed是已经完成.
句子的意思是说只有完成了某样东西,发电站才能供应电能.