Engine 2014: Electricity

1. A When necessary, they should always be dressed with a wire wheel.
2. B They should be filed with a fine-cut file when projections extend beyond the contact surface.
3. C When black silver oxide is present, it should always be removed from the contact surface with coarse sandpaper.
4. D When necessary, they should be spray painted with electrical shellac

Tip: press A-D to answer