The correct response is:
because Confucius believed it is the model for the other four relationships.
In Confucianism, filial piety (xiao) is considered foundational because it emphasizes respect, loyalty, and care for one's parents and ancestors. This virtue is seen as a model for how individuals should conduct themselves in other social relationships, including those between friends, siblings, rulers and subjects, and husbands and wives. By fostering a sense of duty and respect within the family, filial piety helps to cultivate harmony and proper conduct throughout society, thereby serving as a cornerstone for all other virtues in Confucian thought.