If you were working full-time now, you could earn $20,000 per year. Instead, you are working part-time while going to school. In your current part-time job, you earn $5,000 per year. At your school, the annual cost of tuition, books, and other fees is $2,000. The opportunity cost of completing your education is:
a. $2,000
b. $5,000
c. $17,000
d. $20,000
e. $22,000