The correct answer is B) stopping the flow of gas. The reason this is the correct answer is that for a fire involving escaping liquefied flammable gas, the most effective way to extinguish the fire is to stop the source of the gas leak. Cutting off the supply of gas will remove the fuel needed to sustain the fire, effectively extinguishing it. Cooling the gas below the ignition point or cutting off the oxygen supply may not be as reliable or practical in an emergency situation involving a gas leak. The other answer choices, while potentially applicable to other types of fires, are not the most effective approach for a fire involving escaping liquefied flammable gas, where stopping the flow of gas is the primary objective.