单项选择题

The underwater listening system was originally designed ______.

A．to trace and locate enemy vessels
B．to monitor deep-sea volcanic eruptions
C．to study the movement of ocean currents
D．to replace the global radio communications network

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单项选择题

The passage is chiefly about ______.

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

单项选择题

Which of the following is true about the U. S. Navy underwater listening network

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B．It has been replaced by a more advanced system.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.