Answer:
d. attending a movie
Step-by-step explanation:
The opportunity cost of going to a concert is attending a movie because he will utilize all his time in the concert and will have no time left for movie. Also this was the second option in his list.
The opportunity cost of going to concert is the enjoyment time of the movie. If he did not go to a concert he would have watched the movie.
The opportunity cost is the value of one alternative chosen over the other. It may be the value of time, money etc.