A lively classroom may include occasional laughter alongside purposeful learning.
Why A is marked: Natural moments of laughter can indicate comfort and engagement without interrupting the lesson.
Why B and D are weaker: Complete silence is not a reliable sign of learning, while loud discussion may or may not be productive.
Question-quality note: Frequent teacher–student dialogue can also be a feature of a lively classroom. The question should distinguish healthy engagement from noise or entertainment.