The correct answer is C) Class C. Fires that occur in energized electrical equipment, such as switchboard insulation, are classified as Class C fires. This is because Class C fires involve energized electrical equipment, where the fire is fed by the electrical current. The National Fire Protection Association (NFPA) defines Class C fires as those that involve energized electrical equipment, where the electrical non-conductivity of the extinguishing media is of importance. The other options are incorrect because Class A fires involve ordinary combustible materials, Class B fires involve flammable liquids or gases, and Class D fires involve combustible metals, none of which specifically apply to energized electrical equipment fires.