The correct answer is A) stopping the flow of gas. The reasoning for this is that the most effective way to extinguish a fire of escaping liquefied flammable gas is to stop the flow of gas. By stopping the gas supply, you eliminate the fuel source that is feeding the fire, which is the key to extinguishing it. The other options, while potentially helpful, are not as directly effective as cutting off the gas source. Cooling the gas below its ignition point (B) or interrupting the chain reaction (C) may help, but do not address the root cause of the continuous gas supply feeding the fire. Cutting off the oxygen supply (D) is generally more applicable to other types of fires, not liquefied gas fires specifically.