The correct answer is: Armature.
The armature is the rotating part of a DC generator that converts mechanical energy into electrical energy. The armature windings are connected to the commutator, which is a series of metal segments that are insulated from each other. The commutator is in contact with the brushes, which are stationary contacts that are connected to the external circuit. When the armature rotates, the commutator switches the current from one winding to the next, which produces a continuous output voltage.
The critical resistance of a DC generator is the resistance of the armature windings. The critical resistance is the minimum resistance that must be present in the armature windings in order for the generator to produce a voltage. If the resistance of the armature windings is too low, the generator will not produce any voltage. If the resistance of the armature windings is too high, the generator will produce too much voltage and may be damaged.
The field windings are the stationary windings of a DC generator that create the magnetic field that induces a voltage in the armature windings. The brushes are the stationary contacts that are connected to the external circuit and that make contact with the commutator. The load is the external circuit that draws current from the generator.
The field windings, brushes, and load do not affect the critical resistance of a DC generator. The critical resistance is only affected by the resistance of the armature windings.