单选题 How does it happen that children learn their mother tongue so well? When we compare them with adults learning a foreign language, we often find this interesting fact. A little child without knowledge or experience often succeeds in a complete mastery of the language. A grown-up person with fully developed mental powers, in most cases, may end up with a faulty and inexact command. What account for this difference?
What may happen in most eases when a grow-up tries to learn a foreign language?

• A. He succeeds in a complete mastery of the language.
• B. He develops full knowledge of the language.
• C. He develops an inexact command of the language.
• D. He confuses his mother tongue with the foreign languag