Choose the word which is different from the rest.

The answer is B, transistor.

A stereo is a system of two or more loudspeakers that are used to reproduce sound from a single source. A transistor is a semiconductor device used to amplify and switch electronic signals and electrical power. A television is a device that receives and displays moving images and sound. A radio is a device that receives and amplifies radio waves and converts them into sound. A loudspeaker is a device that converts electrical signals into sound waves.

B, transistor, is different from the rest because it is a device, while the others are systems or devices that use devices.