Everyone knows that exercise is important. We all need to exercise. There are many ways to exercise. You can walk, run, swim, skate, or play ball games, but you should remember to exercise in the right ways.

        ①    Before you do any exercise, make sure to warm up for at least five minutes. During warming up, you should extend all parts of your body.

        ②      It's best to exercise twice each week. Thirty minutes each time is enough. Try all kinds of things until you find one, two or even three sports that feel right for you.

        ③    There are a lot of equipments (设备) at fitness centers. The equipments will help exercise your arms, legs and other parts of your body to make you fit. Some people buy equipments for their homes. But it is very expensive.

        ④     If you get hurt when you are doing exercise, don't play again until you are well.

人民代表大会制度是我国的根本政治制度,民主集中制是我国人民代表大会制度的组织和活动原则。下列选项中,能体现民主集中制原则的是（  ）

计算小数加减法，得数的小数部分有0的要把0去掉。（    ）