单项选择题
Under centrifugal pumps are the volute, diffuser, mixed-flow, axial flow and （） or regenerative types.
A.reciprocating B.hydraulic C.turbine D.vane
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.
单项选择题 Manually operated band brakes may be fitted and （） will have a brake arranged to fail-safe.
