封隔器分层压裂有()。
A.单封分层压裂
B.双封分层压裂
C.桥塞分层压裂
D.包括A、B、C
参考答案:D
I_________frustrated when I wasn't sure of the correct answer. [ ]
A. may be
B. used to
C. used to be
D. use to be
丙烯原料罐引丙烯时要()防止丙烯直接进入大量气化冻坏设备。
A、用仪表风升压
B、用工厂风升压
C、用氮气升压
D、用蒸气升压