21. children

22. studying

23. playing

24. school

25. Don't watch too much TV because your mother doesn't want you to watch it.

26. She stayed at home because she didn't feel well.

27. New York is the most exciting city in the world.

28. How long did you learn English?

29. We have known each other for ten years.

30. Harry is an intelligent student in my class.

III. - Skateboarding is my favourite sport. In skateboarding, there are no teams and no rules. You're on your own. And that's why I love it! One minute I'm speeding along the ground, the next minute I'm flying through the air. So I need a lot of skill. I need protective gear to protect me too. Knee pads, elbow pads and my helmet, of course. I think I look cool!