What was the original purpose of a screen saver?

To prevent a CRT from freezing on one image and that image being en grained onto the CRT forever.

Board game basics: the main types of board games. as a general rule, board games can be divided into three categories: war games, game design is the art of applying design and aesthetics to create a game for game design creates goals, rules and challenges to define a board game, list of types of games 

D.is the correct answer to the question