The correct answer is D) High capacity fan. The high capacity fan is used to supply inert gas from a flue gas system to the cargo tanks. This method utilizes a powerful fan to draw the inert gas, typically composed of carbon dioxide and nitrogen, from the flue gas system and push it into the cargo tanks. This ensures an adequate supply of inert gas to maintain a safe, non-combustible atmosphere within the cargo tanks. The other options are incorrect because: A) An inert gas compressor is used to compress the inert gas, not to supply it to the cargo tanks. B) Exhaust gas pressure alone is not sufficient to provide the necessary flow of inert gas to the cargo tanks. C) Natural aspiration, which relies on the natural movement of gases, is not a reliable method for delivering inert gas to the cargo tanks.