Explanation: A short in the armature coils bypasses some windings, effectively reducing the number of active turns. This significantly decreases the back Electromotive Force (EMF) generated by the motor for a given speed. Since back EMF opposes the applied voltage, a lower back EMF means a higher net voltage across the armature. This results in excessive armature current. Excessive current causes increased I²R losses, leading to significant overheating of the motor (making option B incorrect). It also causes excessive sparking at the commutator brushes (making option A incorrect). The high current, combined with the reduced effective turns, diminishes the motor's ability to produce sufficient torque, leading to a reduction of speed, especially when operating under load. Therefore, option C is correct.