根据结构型式,可以把叶片式压气机分为():(1)轴流式(2)活塞式(3)离心式
A.(1)(2)
B.(1)(3)
C.(2)(3)
D.(1)(2)(3)
参考答案:B
— Must they clean and tidy the classroom now?
— No, they . It after school in the afternoon. [ ]
A. mustn't; must clean
B. needn't; must clean
C. mustn't; need be cleaned
D. don't have to; can be cleaned
“民为贵,社稷次之,君为轻”为句话出自()。