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

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热门试题

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

单项选择题

The deep-sea listening system makes use of ______

A．the sophisticated technology of focusing sounds under water
B．the capability of sound to travel at high speed
C．the unique property of layers of ocean water in transmitting sound
D．low-frequency sounds traveling across different layers of water