10) you are faced with the following alternative choices on a friday night: choice a: go to a concert, which costs $30. choice b: go to a party at a friend's house. choice c: go to the library and study economics. it turns out that choice a is your most preferred activity, choice b is your second most preferred activity, and choice c is your least preferred activity, so naturally, you go to the concert. what is the oportunity cost of going to the concert? a) $30 b) $30 plus missing your friend's party. c) $30 plus missing your friend's party plus not studying economics at the library. d) missing your friend's party plus not studying economics at the library.