Please choose the correct ending to complete the given sentence: Computers and Electronics: [header] How to increase your vertical leap [title] Perform calisthenics every day to increase flexibility. [step] Stand with your legs together. Lift yourself onto your toes, then lower yourself down.

Ending1: Try to hold the position for about 30 seconds. Hold for longer if your heart muscle is weakened, or if you find yourself leaning to one side. Ending2: Move slowly to make the muscles work harder. [substeps] For better results, stand on the edge of a curb or a step. Ending3: Focus on keeping your back and head straight. Your back should form a straight line from head to toe without side bending. Ending4: Hold for 1 second, then come back up to center with a straight leg and then repeat. [title] Do it on your stomach three times a day.

Answer format: ending1/ending2/ending3/ending4