Answer:
The correct answer is:
a) nothing - it's FREE
Step-by-step explanation:
opportunity cost refers to the benefit forgone in other to benefit from another alternative.
In this example, the opportunity cost is "nothing", since it was not stated that attending the concert will deprive you of attending the movies when it eventually opens. The concert and the movie do not occur at the same time, hence there is no opportunity cost for attending the concert in place of the movie.
However, if attending the concert meant not being able to attend the movie, then the opportunity cost would have been the cost of the movie ticket.