单项选择题
Operating a rotary pump at speeds in excess of design requirements could cause（）.
A.decreased clearances between rotating parts B.decreased slippage to the suction side of the pump C.air binding in the discharge ports D.erosion and excessive wear
单项选择题 A refrigeration system compressor crankcase is sweating or unusually coldThis is an indication of（）.
单项选择题 When the desired rudder angle is attained by a typical double mm electro-hydraulic steering gear,the（）.
单项选择题 A swing check valve is used in a pipeline to （）.
