The project is designed in this way and once____,nothing can be done to change it.A.startsB.startingC.startedD.having startedonce started是固定用法吗?

The project is designed in this way and once____,nothing can be done to change it.A.startsB.startingC.startedD.having startedonce started是固定用法吗?
The project is designed in this way and once____,nothing can be done to change it.
A.starts
B.starting
C.started
D.having started
once started是固定用法吗?

The project is designed in this way and once____,nothing can be done to change it.A.startsB.startingC.startedD.having startedonce started是固定用法吗?
拜托楼上的不要装懂
这是省略句!一旦主语一致,后边的部分可以把主语和谓语动词中的be省掉!

1 c
不是固定用法，是once的用法
once+过去分词（被动），表示“一旦...就...”