The etiquette system formed during the Western Zhou Dynasty first adopted the method of regulating people's daily behavior standards, and carried this tradition into the upper society and home life. Although the "Western Zhou Dynasty" "does not lower people," the original purpose of establishing the etiquette system is to maintain the interests of slave owners and nobles, strengthened the social hierarchy of slaves, in order to coordinate the relationship within the slave owner class, but after entering the Spring and Autumn Period, with the slave system "the etiquette and music collapsed", the rules of "knowledge down" In the situation of "popularity", this tradition and etiquette system have therefore penetrated into a wider range of social life; it has become a code of conduct and norms widely observed by society. What does this text mainly explains about the etiquette system? ['Throughout ancient Chinese social life.', 'is good for the ruling class.', 'For the benefit of slave owners and nobles.', 'is a tradition of social life.']