This is a test of commonsense with single/multi-choices. Complete the next sentence:

How to do a stability ball knee tuck
Put your exercise ball in an open area.
You should have plenty of free space to move around, and all sharp/heavy objects should be removed so as to minimize the potential for accidents.
Lie face-down on the ball and walk yourself forward on your arms.

Choose your answer from: (i) Twist your knees and knees, and move your belly button in one direction and your abdominal muscles in the other. Stick your right foot in front of your left.; (ii) Immediately use one arm to press your arms up and extend your back straight. Once you have tried this exercise 5 times, go figure out how to stay upright without bending your knees.; (iii) Go slowly, to avoid injuring yourself with the ball. Start by jumping into position with your arms above your head (in a figure-8 position), legs slightly wider than shoulder width apart.; (iv) As your torso comes off the ball your legs should roll onto it, so that you end up with your shins pressed into it and the rest of your body supported by your arms. Make sure to keep your head aligned with your shoulders and hips.;
The answer is:
(iv)