Answer:
Size of the court
Step-by-step explanation:
In the game of tennis, there could be a singles match typically involving just two players, or a doubles tennis which involves four players. The rule modified for the doubles tennis is that a wider court is used since there are more players involved.
Each player can serve the tennis after the fourth game. The server and receiver can stand at any side of the court even though it is ideal that they maintain one side.