Primates need to groom their fur for parasites. Grooming can be either done cooperatively by another ...

Primates need to groom their fur for parasites. Grooming can be either done cooperatively by another indi-vidual or individuals can groom themselves. Grooming oneself requires more time and energy than grooming another individual.
 
  Assume that during an encounter only one individual grooms the other, and that this action would have to be reciprocated at a future encounter. What, according to game theory, is the best strategy if individuals know that they will meet exactly twice in their lifetime?
  a. to groom the other individual; this action will be reciprocated at the second encounter
  b. not to groom the other individual; with a fixed number of encounters, there are no repercus-sions for the second individual not returning the favor
  c. not to groom the other individual; cooperation is always the worst strategy in this system re-gardless of whether the number of future encounters is known or not
  d. to groom the other individual; cooperation maximizes the average benefit for both individuals