The correct answer is D) It puts an excessive load on the bus. Motorization of an AC generator is undesirable because it puts an excessive load on the electrical bus or distribution system. When an AC generator is driven by a motor, it acts like a large load on the electrical system, which can cause instability, voltage fluctuations, and potentially damage other connected equipment. This is why it is generally recommended to use a dedicated prime mover, such as an engine or turbine, to drive the AC generator rather than a motor. The other answer choices are incorrect because: A) Reversing the rotation of the generator itself would not damage the generator. B) High voltage pulses are not a concern with the motorization of the generator. C) The prime mover (the motor) would not be damaged by reversing its rotation, as it is designed to operate in both directions.