Which of the following is a primary function of the crankshaft?

The primary function of the crankshaft is to convert the linear motion generated by the pistons into rotational motion, which is essential for the operation of internal combustion engines. As the pistons move up and down in their cylinders due to combustion, the crankshaft translates that vertical motion into a circular motion. This rotational motion is then used to drive the engine's output, whether it be turning the wheels of a vehicle or powering a generator.

While other options describe functions that are relevant to engines, they do not accurately capture the primary role of the crankshaft. For example, structural support is provided by the engine block and other components, while maintaining constant speed is more about the engine's control systems and throttle management. Lastly, electrical components usually rely on alternators or batteries as power sources rather than the crankshaft directly.