Please choose the correct ending to complete the given sentence: Sports and Fitness: [header] How to do abdominal crunches with angled heels [title] Lie down facing the ceiling with your knees bent and your shoulders, hips, and feet aligned. [step] Flatten your back and clench your abs, clasping your hands together behind your head. [title] Raise your toes up so that your heels press into the ground.

Ending1: [step] This should work your upper thigh muscles; if you do not feel the effort there, try pressing a little harder. [title] Bring your head and shoulders up towards your hips in a typical crunch motion. Ending2: [title] Slowly lean over until your thighs touch the floor. [step] Your legs should be spread out wide to create a triangle shape. Ending3: [step] Keep your upper body flat and engage your abs by flexing them. [substeps] Bring your butt up toward the ceiling as you execute your oblique crunches. Ending4: [step] If you find it difficult to keep your heels firmly against the floor, you may want to try bending over a bit to move your lower back. [substeps] If your knees keep continuing to pull into the ground, you're not balanced enough to keep them there.

Answer format: ending1/ending2/ending3/ending4