3 Circle the correct words. 1 Your muscles need / don't need oxygen to work well for a long time. 2 When you swim, you breathe faster / slower. 3 Swimming makes you fatter / more healthy. 4 When your body works very hard, your muscles can / can't get all the oxygen that they need. 5 You can only run fast for a long / short time. 6 Running fast makes your muscles bigger / smaller. 4 Answer the questions. 1 Why do you breathe faster when you do exercise? 2 What does sweat do? 3 What do your muscles need to work for a long time? 4 What happens when your body works very hard? 5 What exercises can you do for a long time? 6 What exercise can you only do for a short time?

Sure! Here are the correct words circled in your sentences, followed by the answers to the questions:

1. Your muscles need oxygen to work well for a long time.
2. When you swim, you breathe faster.
3. Swimming makes you more healthy.
4. When your body works very hard, your muscles can't get all the oxygen that they need.
5. You can only run fast for a short time.
6. Running fast makes your muscles bigger.

Now, for the answers to the questions:

1. You breathe faster when you do exercise because your body requires more oxygen to fuel your muscles and remove carbon dioxide more efficiently.
2. Sweat helps cool your body down through evaporation. It also helps to regulate body temperature during exercise.
3. Your muscles need oxygen to work for a long time, as it is essential for aerobic energy production.
4. When your body works very hard, your muscles can’t get all the oxygen they need, leading to a build-up of lactic acid and fatigue.
5. Exercises that you can do for a long time typically include activities like jogging, cycling, and swimming at a moderate pace.
6. Exercise that you can only do for a short time includes sprinting or high-intensity intervals, as they require a lot of energy in a short burst.