Which of the following statements is true?
a. The opportunity cost (O.C.) is what you sacrifice when you make a choice or take an action.
b. The O.C. of a choice (or action) we make is everything we sacrifice when we make that choice (or action).
c. In economics, we assume that while firms try to maximize their utility (a measure of satisfaction), consumers try to maximize their profit.
d. All of the above.