阅读理解。 We all need to exercise. Doctors say it is good for us. It makes your heart and body strong. It also gives you more energy. And you will feel better about yourself. It's best to exercise twice a week. Twenty minutes each time is enough. There are many ways to exercise. You can walk, run, play sports, or swim. Many people go to special places to exercise. They are ca1led'fitness centers.' These places have a lot of equipment. Some People buy equipment for their homes. But it is very expensive. Exercising can be fun. Friends can exercise together at a fitness center. Or, they can play sports together. How do you exercise? 1. What is the main idea? [     ] A. Exercise equipment is expensive. B. Playing sports is a good way to exercise. C. Every person shou1d exercise. 2. We should exercise _____. [     ] A. every day B. 20 minutes a week C. twice a week 3. At fitness centers, _____. [     ] A. you can buy expensive equipment B. people can do many kinds of exercising C. it is very expensive 4. Which of these kinds of exercising is not in the article? [     ] A. Dancing. B. Swimming. C. Sports. 5. Which of these sentences about exercising is true? [     ] A. Exercising is expensive. B. Exercise is good for your heart. C. Only doctors exercise.