Describe the operation of a relay.

A relay operates by employing an electromagnet to mechanically control the switching of a circuit on or off. When an electric current flows through the coil of the relay, it generates a magnetic field that attracts a movable armature. This mechanical movement creates a connection between two contacts, completing the circuit and allowing current to flow. The ability to control large amounts of electricity by a smaller current makes relays essential in various applications, including automation and safety systems. This principle of electromagnetic control is fundamental in relay design, making option B the correct explanation of how a relay functions.