Even Groups That Are Largely Self-Sufficient Engage in Exchange with Other

Even groups that are largely self-sufficient engage in exchange with other groups. Anthropologists suggest this is because

A) the need to give to others is biologically determined.
B) there are always some goods or services that one cannot get for oneself.
C) exchange creates and sustains relationships that are necessary for other reasons.
D) most groups have spiritual beliefs that value altruistic behavior.