Suppose there are three things that Bob can do$.$ From most valuable to least valuable those things are: hang out with Louise, take a nap, or go to the wharf. Choosing one of these activities means that he cannot do the others.

What is the opportunity cost of hanging out with Louise?

a$.$ There is no opportunity cost because none of those actions cost money.

b$.$ The value taking a nap plus the value going to the wharf.

c$.$ The value Bob would have gotten from taking a nap.

d$.$ The value Bob would have gotten from going to the wharf.

Clear my choice