阅读理解。 Everyone knows that exercise is important. We all need to exercise. Doctors say it is good for us. It makes your heart and body strong. Children who often exercise are more alert (灵活). That means they do better in tests and schoolwork than those who don't exercise. They are many ways to exercise. You can walk, run, swim, skate, or play ball s. Make sure you exercise in the following ways: You have to like what you are doing. Exercise enough (足够的)  but not too much. It's best to exercise twice a week. Thirty minutes (分钟) each time is enough. Try all kinds of sports until (直到) you find one, two or even three sports that feel right for you. You can exercise at fitness centers. They have a lot of equipment (设备) there. The equipment will help exercise your arms, legs and other parts of your body to make you healthy. Some people buy equipment for their homes. But it's very expensive. 1. the underline word 'fitness centers' in the passage means _____. A. 商务中心 B. 健身中心 C. 医疗中心 D. 购物中心 2. The sport '_____' is not told in the passage. A. playing soccer B. skateboarding C. walking D. running 3. The doctors say that exercise can make your heart and body _____. A. ill B. happy C. strong D. health 4. About 'exercise', which statement of the following is NOT right? A. Thirty minutes' exercise each time is enough. B. You have to exercise too much every day. C. You needn't do all kinds of sports to keep healthy. D. You have to like the sports that you are doing. 5. It's best to exercise _____. A. at fitness centers B. in groups C. in the morning D. twice a week