潜油电泵在空载情况下启动时，（）可起保护作用。
A.保护器
B.分离器
C.单流阀
D.泄油阀
参考答案：C
---I’m sorry. That wasn’t of much help.
---_____. And it was most helpful.
A．Thanks anyway.
B．It doesn’t matter.
C．Of course not.
D．Sure it was.
按照国家标准，火灾分为（）。
A.3类
B.4类
C.5类
D.6类
