Directions：
Read the following text. Choose the best word (s) for each numbered blank and mark A, B, C or D.
       From childhood to old age, we all use language as a means of broadening our knowledge of ourselves and the world about us. When humans first  , they were like newborn children, unable to use this  tool. Yet once language developed, the possibilities for human kinds future  and cultural growth increased.
       Many linguists believe that evolution is  for our ability to produce and use language. They  that our highly evolved brain provides us  an innate language ability not found in lower . Proponents of this innateness theory say that our  for language is inborn, but that language itself develops gradually,  a function of the growth of the brain during childhood. Therefore there are critical  times for language development.
        Current  of innateness theory are mixed, however, evidence supporting the existence of some innate abilities is undeniable.  , more and more schools are discovering that foreign languages are best taught in  grades. Young children often can learn several languages by being  to them, while adults have a much harder time learning another language once the  of their first language have become firmly fixed.
         some aspects of language are undeniably innate, language does not develop automatically in a vacuum. Children who have been  from other human beings do not possess language. This demonstrates that  with other human beings is necessary for proper language development. Some linguists believe that this is even more basic to human language  than any innate capacities. These theorists view language as imitative, learned behavior.  , children learn language from their parents by imitating them. Parents gradually shape their child’s language skills by positively reinforcing precise imitations and negatively reinforcing imprecise ones.