（）are used to digest the sewage to produce innocuous sludge in a biological sewage treatment plant.

A.the temperature and flow quantity of the exhaust gas from M.E
B.the quantity of steam demanded
C.the rotary speed and the cooling water temperature of main engine
D.efficiency of M.E turbocharger

A.purge lube oil from the liquid refrigerant
B.recover water purged from the system
C.separate foul gases from the receiver
D.purge non-condensable gases without losing refrigerant