所有正常工况下只有（）时的井底压力低于静液压力。
A、起管柱
B、下管柱
C、空井
参考答案：A
But for your timely help, I ________ the project as scheduled.
A．couldn’t complete
B．couldn’t have finished
C．can’t have finished
D．can’t finish
三不交工
