The opportunity cost of attending a class at 11:00 a.m. will likely differ from the opportunity cost of attending a class at 8:00 a.m. because

A.
the number and variety of alternatives at 11 a.m. are likely to differ from those available at 8 a.m.
B.
nothing is going on at 8 a.m.
C.
a student's evaluation of any given set of alternatives is likely to be time-sensitive.
D.
both A and C are correct.