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

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单项选择题

A．singleB．singularC．pluralD．compound

A．single
B．singular
C．plural
D．compound

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