Interaction gives learners a chance to exchange ideas and receive feedback.
Why B fits: Small-group discussion requires students to listen, respond, explain, and consider other viewpoints.
Why the others are weaker: A film, expert lecture, or televised classroom programme may be informative, but viewing or listening alone provides fewer opportunities for learners to interact.
Teaching point: Group work is most effective when the task is clear and every learner has a chance to contribute.