【单选题】

The positive pressure relief valves are fail safe devices that bleed fuselage pressure overboard if the aft outflow valve fails closeD.

A、The positive pressure relief valves are fail safe devices. If the aft outflow valve cann’t be closed, these positive pressure relief valves bleed fuselage pressure overboarD.
B、The positive pressure relief valves are fail safe devices. If the positive pressure relief valves fails closed, these aft outflow valve bleed fuselage pressure overboarD.
C、The positive pressure relief valves are fail safe devices. If the aft outflow valve fails closed, these positive pressure relief valves bleed fuselage pressure overboarD.