A、In childhood. B、The earlier, the better. C、When one is mature enough. D、When one has the need and has enough time. D

Some people think that the best time to begin studying a foreign language is in childhood and that the younger you are, the easier it is to learn another language.  There is little evidence, however, that children in language classrooms learn foreign languages any better than people over age fifteen in similar classroom situations.  In fact, adults have many advantages over children: better memories, more efficient ways of organizing information, longer attention spans, better study habits, and greater ability to handle complex mental tasks. Adults see learning a foreign language as necessary for education or career.  In addition, they are particularly sensitive to correctness of grammar and appropriateness of vocabulary: two factors that receive much attention in most language classrooms.
    You can indeed master a foreign language—as lots of adults do. The best time to learn a foreign language is when your need is the clearest and you have sufficient time. If you feel strongly the need to study a foreign language and if you have the time to do it, the best time to begin is now.