Which of the following is not an example of the opportunity cost of going to school?

A、The money a student could have earned by working
if he had not gone to college.;
B、The nap a student could have enjoyed if he had
not attended class.;
C、The party a student could have enjoyed if he had
not stayed in to study for his exam.;
D、The money a student spends on rent for his
apartment while attending school.