Any attempt to trace the development from the noises babies make to their first spoken words lead to considerable difficulties. It is agreed that they enjoy making noises, and that during the first few months one or two noises sort themselves out as particularly indicative (标示的) of delight, distress, sociability, and so on. But since these cannot be said to show the baby's intention to communicate, they can hardly be regarded as early forms of language. It is agreed, too, that from about three months they play with sounds for enjoyment, and that by six months they are able to add new sounds to their store. This self-imitation (自我模仿) leads on to deliberate imitation of sounds made or words spoken to them by other people. The problem then arisen so to the point at which one can say that these imitations can be considered as speech.
It is a problem we need not get our teeth into. The meaning of a word depends on what a particular person means by it in a particular situation; and it is clear that what a child means by a word will change as he gains more experience of the world. Thus the use, at say seven months, of "mama" as a greeting for his mother cannot be dismissed as a meaningless sound simply because he also uses it at other times for his father, his dog, or anything else he likes.
Playful(顽皮的)and apparently meaningless imitation of what other people say continues after the child has begun to speak for himself. I doubt, however, whether anything is gained when parents, cash in on this ability in an attempt to teach new sounds.
Children who start speaking late______.

A. probably do not hear enough language spoken around them
B. often take a long time in learning to listen properly
C. usually pay close attention to what they hear
D. may have problems with their hearing