题目

Why Exercise Is Cool? 1. Exercise Strengthens Muscles Did you ever do a push-up or swing across the monkey bars at the playground?    71    By using your muscles to do powerful things, you can make them stronger. For older teens and adults, this kind of workout can make muscles bigger, too. 2.    72   Can you touch your toes easily without yelling ouch? Most kids are pretty flexible, which means that they can bend and stretch their bodies without much trouble. Being flexible is having “full range of motion,” which means you can move your arms and legs freely without fee细菌有叶绿体。但必须从外界获取营养。（____）