Please choose the correct ending to complete the given sentence: Sports and Fitness: [header] How to do the dead bug exercise [title] Lie flat on your back. [step] Sit down and then engage your abs by pulling them inward towards your back. However, keep in mind that some fitness experts see pulling your abs inward as counterproductive and instead recommend that you brace your abs.

Ending1: In fact, the best way to do this exercise is to lie on your stomach, with your upper body turned slightly outward. [substeps] Practice the exercise two or three times a day for about 12 to 15 minutes at a time. Ending2: If you keep your abs pulled inward, doing this exercise on a carpeted surface (grass or cement floor) is an easier and quicker and more efficient way to perform the exercise. [title] Lift your back up into seated position. Ending3: You can try both options and see which one feels like it is working better. Then, use your abs to gently lower yourself onto your back. Ending4: [substeps] The pros and cons of this exercise are that it can be done with your hands in front of you, and the cons are that it forces you to take deep breaths to get oxygen. Your abs have been shown to work better when you sit upright, so do not worry about keeping your abdominal muscles under control.

Answer format: ending1/ending2/ending3/ending4