When an aircraft station fails to establish contact with the aeronautical station on the designated frequency, it shall _______ .
A.attempt to establish contact on another frequency appropriate to the route
B.attempt to establish communication with other aircraft or other aeronautical stations on frequencies appropriate to the route
C.transmit its message twice on the designated frequencies, preceded by the phrase “Transmitting blind”
D.any one of the above procedures that is practicable
正确答案是D