When it is necessary to open a refrigeration system for repairs and the system will be open for more than a few minutes, the open ends of the system should be （）.

A.combustion control air system
B.supply air system
C.ships service air system
D.low pressure deck air system

A.dry bulb temperature
B.wet bulb temperature
C.saturation temperature
D.water vapor superheat

A.The follow-up gear
B.The rudder angle indicator
C.The synchronous electric transmitter
D.A rudder angle limit switch