A.Volute pump
B.Diffuser pump
C.Regenerative pump
D.All of the above
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A.mixed-flow
B.axial-flow
C.centrifugal
D.displacement
Which of the following operating features do displacement pumps bear if they are working under no-cavitation condition?（）
(1) output is almost directly proportional to speed
(2) they are self-priming
(3) they will develop a discharged pressure equal to the resistance to be overcome, irrespective of speed
A.（1）and（2）
B.（2）and（3）
C.（1）and（3）
D.（1），（2）and（3）
Which of the following pumps will build up a bursting pressure or stall their motors if the discharge valves are closed?（）
(1) gear
(2) centrifugal
(3) screw
A.（1）and（2）
B.（1），（2）and（3）
C.（1）and（3）
D.（2）and（3）
A.providing the impeller with balancing holes
B.the use of symmetrical impeller
C.neither A nor B
D.either A or B
A.throttling the pressure line
B.changing the speed of the rotor
C.either A or B
D.None of the above is true
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