The correct answer is: B. Copper losses
Copper losses are the losses that occur in the windings of a transformer due to the resistance of the copper wire. These losses are proportional to the square of the current, and therefore remain constant irrespective of load changes.
Friction and windage losses are the losses that occur due to the friction of the rotating parts of the transformer, and the windage losses that occur due to the air resistance of the rotating parts. These losses are proportional to the speed of the transformer, and therefore increase with load.
Hysteresis and eddy current losses are the losses that occur due to the magnetic flux in the core of the transformer. These losses are proportional to the square of the flux, and therefore increase with load.
Therefore, the only losses that remain constant irrespective of load changes are copper losses.