As for an oil-fired boiler if at a normal steaming condition and water goes out of sight in gauge glasses the action you should take is: （）
(1) secure oil to fires
(2) increase feed pump pressure

A.latent heat of condensation
B.latent heat of vaporization
C.latent heat of saturation
D.sensible heat of condensation

A.physical state
B.temperature
C.atmospheric pressure
D.sensible pressure

A.The blow down valve
B.The scum valve
C.The air release cock
D.The soot-blower