Which of the listed devices would be installed at a control system air pressure reducing station?（）

A.rate of doing work
B.amount of force needed to overcome friction
C.amount of work accomplished
D.distance through which an object is moved

A.re-adjust the discharge pressure
B.clean the expansion valve screen
C.add refrigerant
D.adjust the expansion valve

A.splash method
B.mechanical force feed lubricators
C.detached sump method
D.internal cooling passages in the crankshafts and connecting rods