21. Why do people usually sing?
A. They like birds.
B. They feel happy.
C. They want to tell a story.
D. They like studying music.
22. Which birds sing the most beautiful songs?
A. Birds in a good temper.
B. Cock birds.
C. Hen birds.
D. Female birds which attract male birds.
23. What warnings does a bird sometimes sing?
A. A warning to keep away.
B. A warning to come quickly.
C. A warning about the approach of people
D. A warning to stop singing.
24. What do most birds usually do if they cannot sing well?
A. warn other birds to go away.
B. give their information in another way.
C. find a wife.
D. fly high in the sky.
25. What is one bird's unusual way of attracting a hen bird?
A. It dances.
B. It spreads out its tail.
C. It searches for a wife.
D. It uses shells and flowers to make a garden.