Which of these sentences uses a semicolon appropriately?
a) although the concert doesn't start for over an hour; most of the fans have already arrived at the concert hall.
b) the concert doesn't start for over an hour; though, most of the fans have already arrived at the concert hall.
c) most of the fans have already arrived at the concert hall; however, the concert doesn't start for over an hour.
d) even though the concert doesn't start for over an hour; however, most of the fans have already arrived at the concert hall.