单选题Gear pumps are （） type because they discharge a near constant amount of liquid regardless of pressure.Apositive displacementBnon-positive displacementCmixed-flowDaxial-flow
单选题
Gear pumps are （） type because they discharge a near constant amount of liquid regardless of pressure.
A
positive displacement
B
non-positive displacement
C
mixed-flow
D
axial-flow
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