The correct response is: because Confucius believed it is the model for the other four relationships.
Confucianism emphasizes the importance of filial piety (respect for one's parents and ancestors) as foundational for moral development and social harmony. It is seen as essential for cultivating virtues in other relationships, such as those between siblings, spouses, friends, and rulers and subjects. Filial piety establishes a framework for how individuals should treat one another with respect and care, making it a cornerstone of Confucian moral philosophy.