The correct answer is: A. Windage loss
Windage loss is a type of mechanical loss in a synchronous motor that occurs due to the friction between the rotating parts of the motor and the air. This loss is proportional to the square of the speed of the motor, and it does not vary with load.
Copper losses are a type of electrical loss in a synchronous motor that occurs due to the resistance of the windings. This loss is proportional to the square of the current flowing through the windings, and it does vary with load.
Any of the above is not the correct answer because it is not specific enough. Windage loss is the only type of loss in a synchronous motor that does not vary with load.
None of the above is also not the correct answer because copper losses do vary with load.