A、Say a few simple words. B、Understand the meaning of their words. C、Form simple statements or sentences. D、Understand the rules

Babies begin learning on their first day of life. (29) Experts say the first three years of a child’s life is the most intensive period of language and speech development. This is the time when the brain is developing. Language and communication skills are believed to develop best in an environment that is rich with sounds and sights. Also, the child should repeatedly hear the speech and language of other people.
    Evidence suggests these are important periods of speech and language development in children. This means the brain is best able to learn a language during this period. Officials say the ability to learn a language will be more difficult if these periods pass without early contact with a language.
    (30) The first signs of communication happen during the first few days of life when a baby learns that crying will bring food and attention. Research shows that most children recognize the general sounds of their native language by six months of age. At that time, a baby also usually begins to make sounds. These sounds become a kind of nonsense speech over time.
    (31) By the end of the first year, most children are able to say a few simple words. But they may not understand the meaning of their words. By eighteen months of age, most children can say eight to ten words. By two years, most children are able to form simple statements, or sentences. By ages three, four and five, the number of words a child can understand quickly increases. It is at this age that children begin to understand the rules of language.
29. What is the passage mainly talking about?
30. What do we know about babies’ learning from the passage?
31. What can most children do by the end of the first year?