Which of the following are considered input devices?

A touchscreen is considered an input device because it allows users to interact directly with what is displayed on the screen by touching it. This interaction can include navigation, selection, and manipulation of on-screen elements, making the touchscreen a key tool for inputting commands and data into a computer system. Input devices are specifically designed to send data and control signals to a computer, which is exactly what a touchscreen does as part of its user interface.

In the context of other choices, a trackball is also an input device because it allows users to control the cursor on the screen using a rolling ball mechanism. Monitors and printers, however, are output devices. Monitors display visual output from the computer, while printers produce hard copy outputs of digital documents, making them incapable of receiving input in the same way that touchscreens and trackballs do.