单项选择题
Which of the listed devices would be installed at a control system air pressure reducing station?（）
A.Moisture separator B.Vacuum breaker C.Lubricator D.Non-return valve
单项选择题 Power is defined as the （）.
单项选择题 To correct the condition of slugging and flooding back in a refrigeration system, it may be necessary to （）.
单项选择题 On small, low pressure, air compressors, the cylinders are usually lubricated by the （）.
