The correct answer is C) Shut off the source of the gas feeding the fire. The preferred method to extinguish an LNG (Liquefied Natural Gas) fire is to shut off the source of the gas feeding the fire. LNG fires are best extinguished by cutting off the fuel supply, rather than using water, foam, or dry chemicals. This is because LNG is an extremely cold, flammable liquid, and applying water, foam, or chemicals may not effectively extinguish the fire and could even cause the fire to spread. Shutting off the gas source is the most effective and safest way to extinguish an LNG fire. The other options, while potentially effective for other types of fires, are not the preferred methods for an LNG fire. Applying water fog or mechanical foam may not be as effective, and using dry chemical ("Purple K") could potentially scatter the flammable gas, causing the fire to spread.