The correct answer is C) primary coil. When the primary winding of a voltage transformer is connected to a steady DC source, there will be no induced voltage in the secondary winding due to the lack of a changing magnetic field. This means that there will be no mutual inductance between the primary and secondary windings. However, the primary coil will still experience self-inductance, which can lead to a current overload in the primary coil as the DC source tries to push current through the inductive primary winding. The other options are incorrect because the core will not experience any issues, the secondary coil will not have any current flowing through it, and the contacts are not the part of the transformer that would be affected.