What is typically installed in expansion slots to enhance a computer's capabilities?

Expansion slots are designed specifically to allow for the addition of various hardware components that enhance a computer's capabilities. One of the most common uses for these slots is to install graphics cards or sound cards. Graphics cards improve visual rendering and gaming capabilities, making them essential for tasks that require advanced graphics processing. Similarly, sound cards enhance audio output, improving the quality of sound for media applications and games.

The other options refer to components that are either not installed in expansion slots or are typically part of the computer's base configuration. Power supplies are essential for providing power to all components in a computer but are housed in a dedicated space within the case rather than in expansion slots. Additional memory units, or RAM, are usually installed in memory slots specifically designed for that purpose, not expansion slots. Network protocols are software-based standards for data transmission and are not physical hardware components that can be installed. This distinction highlights why graphics or sound cards are the correct answer as they are directly associated with the purpose of expansion slots.