Please choose the correct ending to complete the given sentence: Sports and Fitness: [header] How to do reverse crunches [title] Lie flat on your back. [step] Fully extend your legs, with your toes pointing upward and keeping your gaze focused on the ceiling. Your body should form a straight line from head to toe.

Ending1: [title] Lift the dumbbells as high as you can. [step] Try to lift each dumbbell one at a time. Ending2: [substeps] Relax your shoulders and neck to minimize the tension in your upper body. Stretching out on a lightly cushioned surface like a yoga mat or a carpeted section of the floor can make performing the exercise more comfortable. Ending3: [title] Keep your abs tight while preparing for your crunches. [step] Contract and uncoil your muscles as you squat over your back. Ending4: Your body should be straight without going too far, and your body should be in a complete circle. [substeps] Try not to have any discomfort when you start a routine.

Answer format: ending1/ending2/ending3/ending4