A、They are in a good temper. B、They like music. C、They want to say something. D、They sing for enjoyment. CWhat is the main reaso

People usually sing because they like music, or because they feel happy. They express their happiness by singing. When a bird sings, however, its song usually means much more than that-the bird is in a good temper. Birds have many reasons for singing. They sing to give information. Their songs are their language. The lovely songs are sung by male birds. They sing to attract female birds. It is their way of saying that they’re looking for a wife. Birds also sing to tell other birds to keep away. To a bird, his tree, or even a branch of a tree is his home. He does not want strangers to come near him, so he sings to warn them. If a bird can not sing well, he usually has some other means of giving important information. Some birds dance, spread out their tails or make other signs. There is also a special kind of bird which builds a small garden of shells and flowers to attract the female bird.