The correct answer is C) heated gases flowing through ventilation systems. Convection is the transfer of heat through the movement of a fluid, such as air or gases. In the context of a ship fire, convection allows the heated gases from the fire to flow through the ship's ventilation systems, spreading the fire to other areas of the vessel. This is a key mechanism by which fires can rapidly spread on ships. The other answer choices are incorrect because they do not directly address the convection process. Option A describes radiant heat transfer, option B describes liquid fuel spread, and option D describes conduction through the ship's metal structure, none of which are the primary means by which convection spreads a fire.