Children at the babbling stage of language development exhibit what behavior?
they imitate single sounds
the utter single words
they out two words together
they create three-words phrases.

They imitate single sounds

Explanation:

The babbling stage is marked by a variety of sounds that are often used in any of the world's languages, though often not the language the child will later speak. The meaning of this observation is unclear. Some experts say babbling signals the beginning of a child's language communication skills. At this stage, sounds provide the repertoire in which the child will identify the phonemes of his language. On the other hand, the order that sounds appear during the babbling period is generally contrary to what they appear in the child's first words. For example, later consonants and anterior vowels, such as [k], [g] and [i], appear early in children's babbling but later in their phonological development.