Concept:A fuse is a safety device that melts and breaks the circuit when current is too high.Explanation:A fuse contains a thin wire that heats up and melts if the current exceeds a safe level.When it melts, it opens the circuit and stops the flow of electricity, protecting appliances from damage.Capacitors, resistors, and switches do not automatically protect against high currents in this way.Answer:B. fuse.