A．in the act of
B．on the point of
C．at the expense of
D．for the sake of

A．RTCA has ordered that all airlines ban portable electronic devices from being used during "critical" stages of flight.
B．Individual airlines have the right to decide whether or not to ban portable electronic devices during flight.
C．Almost all airlines enforce a total ban of portable electronic devices during flight.
D．Experts have recommended airlines to prohibit passengers from using electronic devices during take-off and landing.