Five sentences related to a topic are given below. Four of them can be put together to form a meaningful and coherent short paragraph. Identify the odd one out. Choose its number as your answer and key it in.

1. Much has been recently discovered about the development of songs in birds.

2. Some species are restricted to a single song learned by all individuals, others have a range of songs.

3. The most important auditory stimuli for the birds are the sounds of other birds.

4. For all bird species there is a prescribed path to development of the final song,

5. A bird begins with the subsong, passes through plastic song, until it achieves the species song.