Which of the Following Situations Could Represent Kin Selection in Action

Which of the following situations could represent kin selection in action?

A) You help your friend with linguistics, and your friend helps you with biology.
B) You help your brother pay for his children's college tuition, even though he may not be able to pay you back.
C) When your mother gets old, you help her pay her property taxes.
D) You inexplicably forget to use birth control, and a child results.