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
It can be inferred from the passage that______.
A．new radio devices should be developed for tracking the endangered blue whales
B．blue whales are no longer endangered with the use of the new listening system
C．opinions differ as to whether civilian scientists should be allowed to use military technology
D．military technology has great potential in civilian use
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 travelling across different layers of water
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