12. The windings of a particular type of DC motor are in its rotor. The magnetic field is reversed during the rotation of the rotor by means of the A. field magnets.
B. commutator.
C. applied power source reversal.
D. armature coil split windings.

B. commutator

Explanation:

The DC motor has a commutator, to keep the rotor rotating. The rotor of the DC motor usually  stop spinning once it aligns with the magnetic field. However, the commutator  would reverse the current through the stator and in this process reverse the magnetic field. This ensures continuous spinning of the rotor.

Therefore, the correct option is "B. commutator."

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