单项选择题
Air line lubricators are used in compressed air systems to lubricate （）.
A.the suction and discharge valves B.tools and equipment served by compressed air C.air line reducing valves D.all of the above
单项选择题 Which of the listed devices would be installed at a control system air pressure reducing station?（）
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 （）.
