The following arc all used to attract passengers EXCEPT ______.

A．charge-free air service
B．a new safety device
C．service on the plane
D．flights within one country

A．a successful airline in the 1980s meets the needs not only of the masses but also of the wealthy passengers
B．it is more comfortable to sit in the back of jet planes
C．business travelers dislike tourists
D．only by specializing in cheap flights can airlines avoid bankruptcy