The correct answer is: A. Wave wound
Equalizer rings are used in wave wound armatures to reduce the circulating current. Circulating current is the current that flows in the armature windings due to the magnetic field produced by the stator windings. This current can cause heating and vibration in the armature, and can also reduce the efficiency of the motor. Equalizer rings are connected between the commutator segments, and they provide a path for the circulating current to flow. This helps to reduce the current in each winding, and it also helps to equalize the voltage across the windings.
Lap wound armatures do not require equalizer rings, because the current in each winding flows in opposite directions. This means that there is no circulating current in a lap wound armature.
Delta wound armatures also do not require equalizer rings, because the current in each winding flows in the same direction. However, delta wound armatures are not as common as lap wound armatures.
Duplex wound armatures are a type of wave wound armature that has two windings per pole. This helps to reduce the circulating current in a duplex wound armature, and it also helps to improve the efficiency of the motor. However, duplex wound armatures are more expensive than lap wound armatures.