Which of the following is a common input device?

The mouse is a common input device because it allows users to interact with a computer's graphical user interface by pointing, clicking, and dragging objects on the screen. It translates the physical movement of the user's hand into cursor movement on the display, facilitating tasks such as selecting files, navigating web pages, and engaging with software applications.

In contrast, the other options serve different functions. A printer is an output device that produces physical copies of digital documents, while a monitor displays visual output from the computer but does not allow for input. Speakers, on the other hand, output sound and do not contribute to entering data or commands into the computer system. This distinction between input and output devices helps clarify why the mouse is recognized as a standard input device.