参考答案：C

解析：[听力原文]26-28 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.26. What is the main reason for birds to sing [试题分析] 本题考查考生对细节的理解。[试题详解] 文中在讲到鸟唱歌有许多理由时，进而指出它们唱歌是为了发出信息，故选C。