描写压气机性能的参数有().
A.增压比和效率
B.级数和通道面积
C.压气机功和功率
D.喘振线和工作线
参考答案:A, C
We _______ pay to get into the concert. It's free.
A.can't
B.mustn't
C.might not
D.don't have to
当供气间发生大量泄露时,操作人员应该马上()。