Please choose the correct ending to complete the given sentence: Sports and Fitness: [header] How to build muscle doing push ups [title] Make sure your form is correct. [step] When performing the push up, your lower back must be straight, i.e., not sagging or arching, and your feet must be shoulder width apart. Your elbows should be tucked close to your body, i.e., at a 20 to 40 degree angle from your abdomen.

Ending1: As you go down, make sure your chest gets as close to the floor as possible. [substeps] Make sure to tighten your abdomen, legs, and buttocks. Ending2: Your knees should be on the floor on each side of your body and your feet should be sticking out forward. Your feet should be pressed toward the ground and your arms should be straight above your head. Ending3: [substeps] Avoid bending forward and curling your upper body (this can create fatigue and joint strain). [title] Focus on doing at least 10 repetitions of this exercise a day. Ending4: Your pecs should be rolled backwards slowly until your arms are extended. Your shoulders should be rolled forward slowly until your arms reach that desired height.

Answer format: ending1/ending2/ending3/ending4