The correct answer is: C. Highest torque braking.
Plugging is a type of braking that occurs when a motor is turned off while it is still rotating. This causes the motor to act as a generator, and the current that is generated creates a braking torque. The braking torque is proportional to the square of the motor speed, so the higher the motor speed, the higher the braking torque.
Option A is incorrect because plugging does not give zero torque braking. In fact, it gives the highest torque braking.
Option B is incorrect because plugging does not give the smallest torque braking. It gives the highest torque braking.
Option D is incorrect because plugging does give the highest torque braking.