The correct answer is C) CO2. Electrical fires should be extinguished using CO2 (carbon dioxide) extinguishers because CO2 is a non-conductive agent that can effectively put out fires in electrical equipment without causing additional damage. CO2 extinguishers work by displacing oxygen and interrupting the chemical reaction of the fire, making them the recommended choice for electrical fires. The other options are not appropriate for electrical fires. Low-velocity fog (A) can conduct electricity and cause further damage, salt water (B) is also conductive, and foam (D) is not effective on energized electrical equipment.