单项选择题
In a hydraulic system, （） are used to protect the system from over pressure.
A.stop valves B.check valves C.safety valves D.reducing valves
单项选择题 A hydraulic motor may be driven by （）.
单项选择题 A high rate of separation between oil and water is favored by （）.
单项选择题 When started, a complete oily water separating unit is first filled （）The oily water mixture is then pumped through the inlet pipe into the coarse separating compartment.
