The Opportunity Cost for Elijah of Going to a Water

The opportunity cost for Elijah of going to a water park is:

A) the price of the admission pass.
B) zero, if he can go with his parents who will pay.
C) zero, if it is raining that day and the water park is closed.
D) the price of the admission pass plus the highest-valued alternative activity Elijah could have done instead.
E) the highest-valued alternative activity Elijah could have done instead.