Which of the following is an example of an input device?

A keyboard is an example of an input device because its primary function is to allow users to enter data and commands into a computer system. Input devices provide the means for users to interact with the computer, facilitating communication between the user and the machine. A keyboard translates the physical actions of the user's fingers into signals that the computer can process, enabling tasks such as typing documents, controlling software applications, and executing commands.

In contrast, other devices listed serve different roles: a monitor displays information generated by the computer, a printer outputs data in a tangible form, and speakers produce sound output. These functions are integral to a computer's operation, but they do not involve the direct input of information as the keyboard does. Therefore, the keyboard stands out as the correct example of an input device in this context.