When an electricity generating plant features shaft-driven generators, what type of propulsor is generally used for main propulsion?

Correct Answer: Option A — Controllable-pitch propeller

Shaft-driven generators require a constant input speed to maintain stable electrical frequency. A controllable-pitch propeller allows the main engine to operate at a constant RPM while varying the blade pitch to adjust vessel speed, ensuring the generator maintains a steady output regardless of the ship's actual speed through water.