1. She was brushing his hair when the phone rang.
2. She was sleeping when I walked into the room.
3. When I saw him, he was preparing to go home.

Độ dài đường cao là:

\(80\times\dfrac{1}{2}=40\left(dm\right)\)

Diện tích của khu vườn là:

\(80\times40=1600\left(dm^2\right)\)

Đáp số: 1600dm²

Part 3

17. celebrated

18. before

19. traditional

20. for

21. pay