The correct answer is: D. Welding
Pole shoes are the parts of a DC generator that direct the magnetic field produced by the field coils. They are made of a magnetic material, such as cast iron or steel, and are shaped like a horseshoe. The pole shoes are fastened to the pole core by welding. This ensures a strong and secure connection between the pole shoes and the pole core.
Rivets are another option for fastening pole shoes to the pole core. However, rivets are not as strong as welding and can be more prone to loosening over time. Counter sunk screws are also not a good option for fastening pole shoes to the pole core. Counter sunk screws do not provide a strong enough connection and can easily come loose. Brazing is another option for fastening pole shoes to the pole core. However, brazing is not as strong as welding and can be more difficult to do.
Welding is the best option for fastening pole shoes to the pole core. Welding provides a strong and secure connection that is not prone to loosening over time. Welding is also relatively easy to do and can be done with a variety of welding equipment.