When was the Tunnel opened to the public

A．a new regulation for all airlines
B．the defects of electronic devices
C．a possible cause of aircraft crashes
D．effective safety measures for air flight

A．They may have been caused by the damage to radio systems.
B．They may have taken place during take-off and landing.
C．They were proved to have been caused by the passengers portable computers.
D．They were suspected to have resulted from electromagnetic interference.