It is C.
Out of 7 people 1 of them has to be on an aisle. He can occupy either of the aisles. So there are two sets of possibilities depending on his seating.
Total = 2 * Number of ways in which 5 people can be seated in 6 chairs.
= 2 * 6! (empty seat can be also considered as an element in the arrangement)
"To dream anything that you want to dream, that is the beauty of the human mind. To do anything that you want to do, that is the strength of the human will. To trust yourself, to test your limits, that is the courage to succeed."
- Bernard Edmonds