The correct answer is option 'C', Watt governor.

Explanation:
The Watt governor is a gravity-controlled type governor. It is named after its inventor, James Watt, who developed it in the late 18th century. This type of governor is commonly used in steam engines to regulate the speed of the engine.

The Watt governor works on the principle of centrifugal force and is designed to maintain a constant speed of the engine by controlling the amount of steam entering the engine. It consists of two rotating balls or weights attached to a vertical spindle. As the engine speed increases, the centrifugal force acting on the balls increases, causing them to move outward. This movement of the balls is transmitted to a lever mechanism, which adjusts the position of the throttle valve to regulate the steam flow.

Key features of the Watt governor:

1. **Gravity-controlled**: The Watt governor is a gravity-controlled governor because the movement of the balls is determined by the force of gravity acting on them and the centrifugal force generated by their rotation.

2. **Centrifugal force**: The centrifugal force acting on the balls is directly proportional to the speed of the engine. As the engine speed increases, the centrifugal force increases, causing the balls to move outward.

3. **Vertical spindle**: The balls are attached to a vertical spindle, which allows them to move freely in a vertical plane. The movement of the balls is translated into a vertical motion of the spindle, which is then transmitted to the throttle valve through a lever mechanism.

4. **Throttle valve**: The throttle valve controls the flow of steam entering the engine. By adjusting the position of the throttle valve, the Watt governor regulates the amount of steam supplied to the engine, thereby controlling the engine speed.

Overall, the Watt governor is a gravity-controlled type governor that uses the principle of centrifugal force to regulate the speed of the engine. It is widely used in steam engines and has been an important component in the development of industrial machinery.