Margo spends $30,000 on one year's college tuition. The opportunity cost of spending one year in college for Margo is:

A. whatever she would have earned had she not been in college.
B. whatever she would have purchased with the $30,000 instead.
C. whatever she would have purchased with the $30,000 plus
D. whatever she would have earned had she not been in college. $30,000.