单项选择题
Domestic water pump is started automatically by （） which operates as the water level falls to a predetermined level.
A.a level controller B.a temperature switch C.a pressure switch D.a floating ball
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.
单项选择题 The （） is used for hauling in or letting out the wires or ropes.
