Concept:Language learning after puberty becomes difficult because the brain has already fully acquired the first language, making it harder to learn a new one implicitly.Explanation:Young children learn languages naturally by listening and imitating native speakers. This implicit learning is most effective before puberty. After puberty, the rules, grammar, and tone of the mother tongue (L1) are firmly established. When learning a second language (L2), interference from L1 occurs, causing difficulty in acquisition. Adults cannot replicate the childhood environment, so explicit learning replaces implicit absorption. Thus, acquiring a new language after puberty is challenging.Answer:D. Difficulty in acquisition