The correct answer is D) AC synchronous motor. In an AC propulsion drive system with no rotor slip, the motor used would be an AC synchronous motor. Synchronous motors operate at a constant speed that is synchronized with the frequency of the AC power supply, allowing for precise control of the propeller speed. This makes them well-suited for propulsion applications where maintaining a consistent, efficient speed is important. The other options are not correct because: A) AC squirrel cage induction motors have some inherent rotor slip, B) AC wound rotor induction motors also have rotor slip, and C) AC/DC universal motors are not typically used in large-scale propulsion systems.