SORU: boşluğa uygun düşen cümleyi bulunuz
Your heart is a muscle. It works hard, pumping blood every day of your life. You can help this important muscle get stronger by doing aerobic exercise. ----. So aerobic exercise is a kind of activity that requires oxygen. When you breathe, you take in oxygen, and, if you're doing aerobic exercise, you may notice you're breathing faster than normal.