The correct answer is C. either A.C. or D.C.
A universal motor is a type of electric motor that can run on either alternating current (AC) or direct current (DC). It is a series-wound motor, which means that the field winding and the armature winding are connected in series. This type of motor is often used in power tools, vacuum cleaners, and other appliances.
The advantage of a universal motor is that it can run on either AC or DC power. This makes it a versatile motor that can be used in a variety of applications. However, the disadvantage of a universal motor is that it is not as efficient as other types of motors.
Option A is incorrect because a universal motor can run on AC power. Option B is incorrect because a universal motor can run on DC power. Option D is incorrect because a universal motor can run on either AC or DC power.