The correct answer is: C. Dynamic braking.
When the terminals of armature of D.C. motor are interchanged, the motor will act as a generator. The generator will then produce a braking torque, which will slow down the motor. This type of braking is called dynamic braking.
Regenerative braking is a type of braking in which the motor is used to generate electricity, which is then used to power other loads or to charge a battery. Plugging is a type of braking in which the motor is connected to a power source in such a way that the current flows in the opposite direction to the normal direction of current flow. This causes the motor to act as a generator, and the generator produces a braking torque.
None of the above is not the correct answer because dynamic braking is a type of braking that occurs when the terminals of armature of D.C. motor are interchanged.