Katie and Rob are seeing a marriage counselor, Dr. McMurray, to ask her advice about how to save their relationship. Dr. McMurray tells them that the reason they are having trouble is because "neither of you perceive that you are getting as much out of the relationship as you are putting into it.". This statement indicates that Dr. McMurray is a proponent of

a. homogamy

b. cohabitation.
c. exchange theory.
d. the family life cycle.

c