The correct answer is C) direct air admission. Large, direct reversing, main propulsion diesel engines on ships typically use direct air admission as the starting system. This is because direct air admission provides the necessary power and torque to turn over and start these large, heavy diesel engines. Hydraulic or electric starting motors may not have the capacity to effectively start these massive engines. Additionally, vane type air motors are more commonly used for smaller auxiliary engines, not the main propulsion diesels. The direct air admission system uses compressed air, stored in high-pressure tanks, that is directly admitted into the engine cylinders to turn the crankshaft and start the engine. This method is reliable, powerful, and well-suited for the demands of large, reversing main propulsion diesels on ships.