=>
B/
I/
1. C inexpensive = cheap
2. A (adj + N)
3. B người tham gia
4. A thanks to : nhờ
5. C in competition with : thi đấu với
6. B make a choice : chọn
7. A tình nguyện
8. B increases 
9. D ought to V = should V

10. B freely
II/
2. Brown plays soccer well.
3. Yan cooks well.
4. He drives carelessly. 
5. She dances skillfully.
6. She makes (a) dress carefully.
7. I swim badly.
8. My mother cycles slowly.
9. These children run quickly.
10. My father drives safely.

III/
1. watching
2. became
3. to have
4. allows
5. to wash
6. play
7. buy
8. not to eat

IV/
1. Would you like to play soccer with us? - Yes, I'd love to.
2. Would you like to have a walk with me? - I'm sorry. I'm busy now.
3. Would you like to go swimming? - Yes, I'd love to.
4. Would you like to play table tennis? - Yes, I'd love to.
5. Would you like to play video games? - No, thanks.