Chris has a one-hour break between classes every Wednesday. Chris can either stay at the library and study or go to the gym and work out. The decision Chris must make is:
A.
not an economic problem because neither one costs money.
B.
not an economic problem because it's an hour that is wasted no matter what Chris does.
C.
an economic problem because the tuition Chris pays covers both the gym and the library.
D.
an economic problem because Chris has only one hour during which he can study or work out.