Armature that revolves between two poles of magnet in an ac generator and plays a prime role in converting mechanical energy into electrical. An AC generator works on the principles of electromagnetic induction.
When the armature rotates in between two magnets facing each other with opposite polarities, it rotates on the axis which is perpendicular to the magnetic field's direction.
With this, an electromotive force (emf) is induced in the armature and thus, the electric current flows through the rings to the wires and we get an ac current. Hence, the prime role in producing the ac current in the generator is done by the armature and its rotatory motion.
There is no such thing as an AC Generator, if its a generator, its DC. I think you are talking about an AC Alternator, in which case the answer would be -wrong answer, deleted-
