单项选择题
Increased internal leakage, in addition to poor hydraulic system response,and inadequate lubrication, is the result of （）.
A.pump bearings in poor condition B.excessively worn actuator-piston packing C.broken directional control valve centering springs D.low hydraulic oil viscosity
单项选择题 Most solenoid valves are actuated by （）.
单项选择题 When normal operating pressure is applied to the hydraulic oil used in a high-pressure system, the oil （）.
单项选择题 If the refrigeration compressor crankcase is sweating, the cause may be due to （）.
