单项选择题
In general, （） is suitable for delivering small quantifies at high pressure.
A.reciprocating pump B.gear pump C.centrifugal pump D.vane pump
单项选择题 Under centrifugal pumps are the volute, diffuser, mixed-flow, axial flow and （） or regenerative types.
单项选择题 Domestic water pump is started automatically by （） which operates as the water level falls to a predetermined level.
单项选择题 In cargo crane, （） for lifting the load.
