Imagine a Primate Caregiver Who Helps Raise a Conspecific's Offspring

Imagine a primate caregiver who helps raise a conspecific's offspring. Such caregiving reduces her fitness by 50% and increases the fitness of the conspecific by 50%. According to Hamilton's rule, is there a type of group in which this behavior will be favored by kin selection?

A) Yes, this behavior will be favored by kin selection in groups where all of the siblings are full siblings.
B) Yes, this behavior will be favored by kin selection in groups where all the siblings are half siblings.
C) No, this behavior is not likely to evolve in any group unless there are explicit kinship systems available, such as in humans.
D) No, there are no group structures of primates that would favor this behavior.