What type of device is necessary for connecting multiple monitors to a single computer?

A graphics card is essential for connecting multiple monitors to a single computer because it provides the necessary processing power and output ports required to drive multiple displays. Modern graphics cards are designed to handle the increased graphical demands and offer various types of video outputs, such as HDMI, DisplayPort, and DVI, enabling seamless connections to multiple monitors.

In contrast, a video splitter can duplicate the output of a single video signal, allowing the same content to be displayed on multiple monitors, but it doesn't allow for independent screens or an extended display setup. A network hub is primarily used to connect multiple devices within a network and is not relevant for video output or display connections. Similarly, a USB hub expands the number of USB ports available on a computer but does not relate to connecting monitors directly, as it does not handle video signals.

Thus, a graphics card is the appropriate device as it facilitates the complex needs of multitasking across several screens, which is essential for improved productivity, gaming, and extensive visual projects.