The correct answer is B) Shut off the leak. The reasoning behind this is that the first priority in extinguishing an LPG (liquefied petroleum gas) fire caused by an escaping gas is to stop the source of the fuel. Shutting off the leak will cut off the supply of gas, which is the primary fuel for the fire. This removes the source of the fire, allowing for more effective extinguishing efforts. The other options are not the best first actions. Calling the fire department is important, but should be done in parallel with shutting off the leak. Using a chemical foam extinguisher or water spray may temporarily suppress the flames, but the fire will continue to burn as long as the gas is leaking. Addressing the leak source is the critical first step in properly extinguishing an LPG fire.