This is a test of commonsense. Complete the next sentence:

How to serve a tennis ball
Get in position.
Before you begin to serve the ball, you have to stand behind the baseline, on the side opposite the service box where you'll be serving. You should stand sideways, pointing your left foot to the opposite post of the net, with your right foot being parallel to the court.
For singles, stand close to the center mark. For doubles, stand farther toward one side, depending on what type of serve you plan to execute and the strategy you and your partner have planned.