Final answer:
Screensavers protect a computer monitor's screen from 'burning in' by changing the display at short intervals.
Step-by-step explanation:
The correct answer is A) Screensaver. A screensaver is a moving image that appears on a computer monitor when it is idle for a certain period of time. Screensavers were originally created to prevent the permanent burn-in of images on older CRT monitors, where prolonged display of static images could cause the image to be permanently etched onto the screen. By regularly changing the display at short intervals, screensavers help to avoid burn-in on computer monitors.