降低转速运行能有效的降低离心泵的（）。
参考答案：汽蚀余量
Lucy: What's your father?
John: [ ]
A. He is in the room.
B. He has a big family.
C. He is a doctor.
D. He likes sports.
三大宗教之所以成为世界宗教的原因和特点？
