Concept:A magnetic relay is a switching device that uses one circuit to control another safely.Explanation:A magnetic relay works by allowing a small current in one circuit to control a larger or more dangerous current in another circuit.When the control circuit is activated, it creates a magnetic field that operates the switch in the second circuit.This prevents a person from directly handling the large or dangerous current.Therefore, the device described is the magnetic relay device.Answer:B. Magnetic relay device