The correct answer is C) Carbon dioxide system. Carbon dioxide (CO2) systems are well-suited for fighting fires in enclosed spaces like a ballast control room. CO2 systems effectively smother the fire by displacing oxygen, which is necessary for combustion. They are also effective at extinguishing fires involving electrical equipment without causing damage. In contrast, other options like dry chemical or water-based systems may not be as effective or appropriate for an electrical fire in a confined space.