A vane pump belongs to （） according to its working principle.

Through a （） pump, the liquid is transferred from the suction to the discharge by the mechanical variation of the volume of a chamber or chambers.

A.positive displacement
B.ejector
C.centrifugal
D.air compressor

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The gear and screw pumps are classified as （）.

A.variable stroke pumps
B.multistage pumps
C.positive displacement pumps
D.triple-ported pumps

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