Answer: Going to the concert.
Explanation: The opportunity cost is simply the loss incurred by choosing a certain option over another. It is simply the cost of the opportunity forgone. In the scenario above, There are three choices : A wrestling match, a basketball match and a concert. However, Josh decision was considering two of the choices ; the wrestling match and the concert. Therefore, if Josh eventually ends opts for the wrestling match, then the opportunity forgone or cost will be the CONCERT.