Why Are Rotating Credit Associations Common in Societies with a Traditional

Why are rotating credit associations common in societies with a traditional sharing system?

A) You are obliged to help when others ask for money, so it's easier to save if you have an obligation to save for your contribution.
B) Rotating credit associations are by nature an altruistic venture, with individual contributors receiving little in return.
C) Societies with traditional sharing systems rarely have formal banking institutions, so there is no alternative way to save money.
D) Rotating credit is a complex version of generalized reciprocity, which has its roots in traditional sharing systems.