The correct answer is B) shut off the leak. The reasoning behind this is that for a liquefied gas fire, the first priority is to stop the source of the fire, which is the escaping gas. Shutting off the leak will cut off the fuel supply and help contain the fire. The other options are not the best first actions - using water spray may not be effective, calling the fire department takes time, and using a chemical extinguisher may not address the root cause of the leak. Shutting off the leak is the most direct and effective first step in extinguishing a liquefied gas fire.