The correct answer is D. Windage losses.
Windage losses are caused by the friction of the air moving past the rotating parts of the motor. These losses are proportional to the square of the speed of the motor and the surface area of the rotating parts.
Eddy current losses are caused by the circulating currents that are induced in the stator core by the magnetic field of the rotor. These losses are proportional to the square of the frequency of the current and the square of the permeability of the core material.
Iron losses are caused by the hysteresis and eddy current losses in the stator core. Hysteresis losses are caused by the reversal of the magnetic field in the core. Eddy current losses are caused by the circulating currents that are induced in the core by the magnetic field.
Copper losses are caused by the resistance of the stator windings. These losses are proportional to the square of the current flowing through the windings.
Therefore, windage losses are the only losses that are not dissipated by the stator core surface in a synchronous motor.