The correct answer is C. Watt.
A watt (W) is a unit of power in the International System of Units (SI). It is defined as one joule per second, or one newton-meter per second. Power is the rate at which energy is transferred or converted.
A henry (H) is the SI unit of inductance. It is defined as the inductance of a closed circuit in which an electric current of one ampere produces a magnetic flux of one weber per turn.
A coulomb (C) is the SI unit of electric charge. It is defined as the charge transported by a constant current of one ampere in one second.
A watt-hour (Wh) is a unit of energy. It is equal to the energy expended by a power of one watt in one hour.
In conclusion, the S.I. unit of power is the watt.