The correct answer is C. Hunting is the repeated and sometimes rhythmic variation of speed due to over-control by the governor. The key is that hunting refers to the governor's tendency to overcorrect speed changes, leading to oscillations in the prime mover's speed. This is caused by the governor's response being too aggressive, resulting in it repeatedly overshooting the desired speed. The other options are incorrect because they do not accurately describe the meaning of hunting in the context of prime mover speed control governors. Option A describes a lack of governor power, option B describes transient speed changes, and option D describes the dead band or threshold before the governor initiates a correction, none of which capture the definition of hunting as an oscillation due to over-control.