What function does a governor serve in a vehicle?

The governor in a vehicle primarily serves as a speed controller. Its main function is to regulate the engine's speed to maintain it within a preset limit. This is crucial for safety and efficiency, as it prevents the vehicle from exceeding safe speed thresholds. Additionally, it often interacts with the throttle to control how much fuel and air mix in the engine, directly influencing acceleration and performance.

While options A and C describe aspects that may relate to a vehicle's operation—such as starting it without using the throttle or regulating fuel delivery—they are not the primary functions of a governor. A governor primarily focuses on speed control, but it can also indirectly affect fuel regulation by limiting engine power, which ties back to maintaining the desired speed.

Thus, the governor's role as a speed controller is fundamental and encompasses elements of fuel regulation as a secondary effect, making it an essential component in vehicle operation.