You Are Given a Ticket to a Bob Dylan Concert

You are given a ticket to a Bob Dylan concert with a face value of $50. You only value the ticket at $40, sell it to a friend for $40, and attend a U2 concert priced at $60. The opportunity cost of attending the U2 concert is:

A) $20 worth of alternative goods and services.
B) $40 worth of alternative goods and services.
C) $50 worth of alternative goods and services.
D) $60 worth of alternative goods and services.