How long does the man have to wait for the text train

A．an effort to protect an endangered marine species
B．the civilian use of a military detection system
C．the exposure of a U. S. Navy top-secret weapon
D．a new way to look into the behavior of blue whales

A．It is now partly accessible to civilian scientists.
B．It has been replaced by a more advanced system.
C．It became useless to the military after the cold war.
D．It is indispensable in protecting endangered species.