21、A healthy diet and regular exercise may help to prevent obesity among children. Take Li Ming for example.

Li Ming used to be a healthy boy. But over a year ago, he got into the habit of eating a lot of junk food and snacks. Besides, he spent a lot of time lying on the sofa, watching TV, and did little exercise. As a result, he put on so much weight that he found it difficult to climb the stairs.

So Li Ming decided to change the unhealthy life style. He began to have a balanced, healthy diet. He also took part in various sports activities such as swimming, skating, running and playing basketball. Months later, Li Ming became as fit as before.