The correct answer is A. Horn gaps.
A horn gap is a type of surge arrestor that is used to protect electrical equipment from high voltage surges due to lightning and switching. It consists of two metal horns that are separated by a small gap. When a high voltage surge occurs, the electric field between the horns causes a spark that bridges the gap. This spark discharges the surge and protects the equipment.
Thermal overload relays are used to protect electrical equipment from overheating. They work by detecting the temperature of the equipment and opening the circuit if the temperature gets too high.
Breathers are used to prevent the build-up of pressure inside electrical equipment. They allow air to flow in and out of the equipment, preventing the pressure from becoming too high.
Conservators are used to absorb oil that leaks from electrical equipment. They contain a filter that traps the oil, preventing it from contaminating the environment.
Here is a diagram of a horn gap:
The two metal horns are connected to the electrical equipment that is being protected. The gap between the horns is filled with a gas, such as air or sulfur hexafluoride. When a high voltage surge occurs, the electric field between the horns causes a spark that bridges the gap. This spark discharges the surge and protects the equipment.