This is a test of commonsense with single/multi-choices. 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.

Choose from: [i] Your eyes should be directly ahead of your net, with your right foot always beside the ball. In certain situations, it might be necessary to increase the distance between the two posts to get the ball to your ideal location. [ii] In regulation tennis, the diamond stumps on each side of the net create a discrete seven foot wide gap between the two posts. This is where you can set the ball to make a split. [iii] 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. [iv] You should be in a squatting position, with your weight on your right foot and the ball pointing down at you. Make sure that you have been sitting upright in your squat position for at least 20 seconds before pushing up the serve and serving it.
The answer is:
[iii]