Choose the most correct statement: O a. In a generator a counter torque can be produced, due to current flowing through the coils of the armature in the presence of an constant external magnetic field, which enhances the rotation of the armature. O b. In a generator a counter torque can be produced, due to a constant external magnetic field, which opposes the rotation of the armature. O c. In conductors, eddy currents can arise due to the presence of a constant magnetic field, and will cause the conductor to heat up. O d. In conductors, where there are no well-defined paths for currents to flow, eddy currents can arise in the conductor when a changing magnetic flux is experienced, and will cause the conductor to heat up. O e. In a dc motor a back EMF can be induced, due to a changing magnetic flux through the coils as the armature rotates, which enhances the rotation of the armature. O f. In a dc motor a back EMF can be induced, due to a constant external magnetic field, which opposes the rotation of the armature