The correct answer is C) power ventilation. Regulations require that pump rooms on tank vessels carrying grade C liquid cargo with machinery spaces below the freeboard deck be ventilated with power ventilation. This is because grade C liquid cargoes, such as gasoline or other flammable liquids, require positive mechanical ventilation to prevent the buildup of flammable vapors. Power ventilation, using fans or blowers, is necessary to ensure adequate air circulation and removal of any hazardous vapors that may accumulate in the pump room. The other options, such as gooseneck vents or multiple ducts, are not sufficient to provide the level of ventilation required for these types of hazardous cargo spaces.