单项选择题
A.permits the passage of vapor but not of flame B.prevents the passage of flammable vapors C.prevents inert gas from leaving a tank D.permits vapors to exit but not enter a tank
A.A load on top system B.Direct line system C.Circle line system D.An inert gas system
A.Evaporation B.Dispersion C.Emulsification D.Drifting