Please choose the correct ending to complete the given sentence: Health: [header] How to keep your knees from popping and cracking [title] Use calf releases to lengthen muscles. [step] To perform this exercise, sit on the floor. Place a tennis ball under one calf.

Ending1: Grip the end of the tennis ball with your hands. Carefully roll your knee up so it touches the top of the tennis ball. Ending2: Place your left foot on top of the ball and support the weight of your body. Run your hands over your legs to help stretch them and stop your knee crushing. Ending3: Place your other leg on top of the ball. Direct your weight onto the ball, wrapping your ankle and shin around it until you feel tension in your shins. Ending4: Put your other leg on top of the first leg. Roll your calf up and down on the tennis ball.

Answer format: ending1/ending2/ending3/ending4