Which one is not an input device?

The correct answer is C. Speaker.

A keyboard is an input device that allows a user to input text into a computer or other electronic device. A mouse is an input device that allows a user to move a cursor on a computer screen and select items. A scanner is an input device that allows a user to scan images or documents into a computer. A speaker is an output device that allows a user to hear sound from a computer.

A speaker is not an input device because it does not allow a user to input data into a computer. Instead, it is an output device that allows a user to hear sound from a computer.