阅读理解　　　 Long before they can actually speak, babies pay special attention to the speech they 　　　 hear around them. Within the first month of their lives, babies'' responses to the sound of 　　　 the human voice will be different from their responses to other sorts of auditory stimuli. They will stop crying when they hear a person talking, but not if they hear a bell or the (5)　 sound of a rattle. At first, the sounds that an infant notices might be only those words that 　　　 receive the heaviest emphasis and that often occur at the ends of utterances. By the time 　　　 they are six or seven weeks old, babies can detect the difference between syllables 　　　 pronounced with rising and falling inflections. Very soon, these differences in adult stress 　　　 and intonation can influence babies'' emotional states and behavior. Long before they (10)　 develop actual language comprehension, babies can sense when an adult is playful or 　　　 angry, attempting to initiate or terminate new behavior, and so on, merely on the basis of 　　　 cues such as the rate, volume, and melody of adult speech. 　　　 Adults make it as easy as they can for babies to pick up a language by exaggerating 　　　 such cues. One researcher observed babies and their mothers in six diverse cultures and (15)　 found that, in all six languages, the mothers used simplified syntax, short utterances and 　　　 nonsense sounds, and transformed certain sounds into baby talk. Other investigators have 　　　 noted that when mothers talk to babies who are only a few months old, they exaggerate 　　　 the pitch, loudness, and intensity of their words. They also exaggerate their facial 　　　 expressions, hold vowels longer, and emphasize certain words. (20)　 More significant for language development than their response to general intonation is 　　　 observation that tiny babies can make relatively fine distinctions between speech sounds. 　　　 other words, babies enter the world with the ability to make precisely those perceptual 　　　 discriminations that are necessary if they are to acquire aural language. 　　　 Babies obviously derive pleasure from sound input, too: even as young as nine months (25)　 they will listen to songs or stories, although the words themselves are beyond their 　　　 understanding. For babies, language is a sensory-motor delight rather than the route to 　　　 prosaic meaning that it often is for adults.