Singing and dancing are a common phenomenon among all human clan tribes, and the great advantage it has created is to enable the population to maintain unity, resolve various internal disputes, and be able to defend their territory more effectively. For the above conclusions to be true, which of the following must be added as a premise? ['Singing and dancing have the effect of making all participants gradually forget the conflicts with others and get along peacefully.', 'Singing and dancing have the emotional and exciting effect of mobilizing all participants.', 'Singing and dancing have the effect of forgetting class differences and hierarchical relationships among all participants.', 'Singing and dancing are psychologically soothing and can make all participants forget about reality.']