The correct answer is C) The motor is started as an induction motor. In an electric propulsion drive system using a large polyphase synchronous main propulsion motor, the motor is typically started as an induction motor. This allows the motor to develop the necessary starting torque to overcome the inertia of the propeller and shaft. During the starting process, the field winding is not energized, and the motor operates as an induction motor, drawing a high starting current. Once the motor reaches a sufficient speed, the field winding is then energized, and the motor transitions to synchronous operation. The other options are incorrect because: A) Resistance is not gradually added to the rotor circuit, as this would be the starting method for a wound-rotor induction motor, not a synchronous motor. B) The starting current is not held below the rated current, as the high starting current is necessary to develop the required starting torque. D) The field winding is not energized for starting purposes only, but rather is energized after the motor has reached a sufficient speed to transition to synchronous operation.