From 8 to 11 P

From 8 to 11 p.m., Sam can either attend a basketball game, a hockey match or the symphony. Suppose that Sam decides to attend the hockey match and thinks to herself that if she did not go to the match she would go to the symphony. Then the opportunity cost of attending the hockey match is

A) going to the symphony.
B) going to the symphony and the basketball game.
C) three hours of time.
D) going to the basketball game.