Identify the topic sentence of the paragraph. (1)The behavior of animals is largely what we call "automatic" or "instinctive." (2)Gi ven certain environmental conditions a female bird will start building a nest. (3)Other female birds of the same species will carry out the identical activity at the same time. (4)This behavior happens when there is a proper stimulus; that is, something in the environment automatically stimulates the bird to act in a certain way. (5)A great deal of a bird's life is controlled by patterns of behavior which are built into its biological system much as information is programmed into a computer. (6)If the stimulus is present, the behavior will automatically follow. (7)For example, a female bird knows she must sit on her eggs until they hatch. (8)If china eggs are substituted for her own eggs, she will continue to sit on them, waiting for the artificial eggs to hatch. She cannot behave in any other way.