The correct answer is: A. both D.C. and A.C.
An induction wattmeter is a type of wattmeter that can be used to measure both direct current (DC) and alternating current (AC) power. It does this by using two coils of wire, one of which is fixed and the other of which rotates. The fixed coil creates a magnetic field, and the rotating coil cuts through this field. This induces a current in the rotating coil, which is proportional to the power being measured.
Induction wattmeters are typically used in industrial settings where both DC and AC power are present. They are also used in some home appliances, such as refrigerators and air conditioners.
Option B. D.C. only is incorrect because induction wattmeters can also be used to measure AC power.
Option C. A.C. only is incorrect because induction wattmeters can also be used to measure DC power.
Option D. any of the above is incorrect because induction wattmeters are not suitable for measuring all types of power. They can only be used to measure power that is in the form of an alternating current.