In 2008, the world's airlines reported an increase in the total number of passengers carried, but a decrease in total revenues, even though prices of airline tickets on all routes remained unchanged from the year before.

Which of the following resolves the paradox described above?

A. The airline industry was a victim of the recession in 2008.
B. Total passenger miles were up in 2008.
C. Fuel costs remained constant from 2007 to 2008.
D. Passengers traveled shorter distances on less expensive flights in 2008.
E. No new aircraft were purchased by any carrier in 2008.