A、Strong activity. B、Exercise for half an hour. C、Use all your strength. D、Do moderate exercise. D

When starting an exercise program, one of the biggest mistakes people make is doing too much too soon. Too much exercise may later result in injury or painful muscle ache. Each exercise session should include a warm-up, the dynamic exercise, and a cool-down period. (17)The warm-up of five minutes should consist of moderate activity that will gradually increase your heart and breathing rate. These prepare the body for vigorous activity by increasing breath and body temperature. A warm-up will reduce the risk of injury during the exercise period.
    After the warm-up, begin the dynamic exercise. At first a period of 15-20 minutes is enough. Gradually increase the amount of exercise time as your physical energy increases. You should exercise at a moderate, not too much intensity. Don’t push yourself until you are about to collapse.(18)If you exercise regularly, you’ll be able to increase the strength and duration of the exercise activity without becoming totally tired.
    After the exercise period, allow your body about five minutes to cool down. Walk around and give your body time to relax gradually. Don’t stand still or lie down immediately after exercising. Stretch at the end of your cool down to increase your flexibility and reduce injury.