当燃油油面低于活门时，通风导管内的排放浮子活门和通风通道使通风系统内的燃油排放到油箱。
A The drain float valves in the vent tubes and the vent channels dilute the fuel in the vent system to drain out of the tank when the fuel face is lower than the valve.
B The drain float valves in the vent tubes and the vent channels permit fuel in the vent system to drain into the tank when the fuel level is lower than the valve.
C The drain float valves in the vent tubes and from the vent channels allow the fuel in the vent system to drain into the tank when the fuel quantity is lower than the valve.