Why Is the Concept of Reciprocal Altruism Fundamentally Paradoxical

Why is the concept of reciprocal altruism fundamentally paradoxical?

A) Because altruistic behavior - true altruistic behavior - has been found by research to be nonexistent since there is no action without a desire for reward.
B) Because the concept of expecting to be repaid for an altruistic action negates the altruistic characteristic of the action in the first place.
C) Because it is not possible for altruistic behaviors to be bidirectional. They can only go from one person to another, and cannot be "repaid."
D) Because the human animal is incapable of engaging in distinctly cooperative behavior; research suggests that egoism is the norm for all actions.