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
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A.a spring
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C.the force of gravity
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单项选择题
When normal operating pressure is applied to the hydraulic oil used in a high-pressure system, the oil （）.
A.viscosity will decrease
B.volume will increase
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A.a shortage of refrigerant
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