下列泵中额定排压（或压力比）与转速有关的是（）。
A.往复泵
B.螺杆泵
C.水环泵
D.齿轮泵
参考答案：C
― May I take your order now?
―_________
― OK, I'll come back in a few minutes. [ ]
A. No, we need more time.
B. Could you bring us the bill?
C. Yes, here it is. Thank you.
D. Sure, we'd love to.
进站色灯信号机显示方式（四显示自动闭塞区段除外）中一个绿色灯光意义是什么？
