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  3. It is hard to track the blue whale, the ocean’s largest creature ,which has almost been killed off by commercial whaling and is

It is hard to track the blue whale, the ocean’s largest creature ,which has almost been killed off by commercial whaling and is

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问题    It is hard to track the blue whale, the ocean’s largest creature ,which has almost been killed off by commercial whaling and is now listed as an endangered species. Attaching radio devices to it is difficult, and visual sightings are too unreliable to give real insight into its behavior.
   So biologists were delighted early this year when, with the help of the Navy ,they were able to track a particular blue whale for 43 days, monitoring its sounds. This was possible because of the Navy’s formerly top-secret system of underwater listening devices spanning the oceans.
   Tracking whales is but one example of an exciting new world just opening to civilian scientists after the cold war as the Navy starts to share and partly uncover its global network of underwater listening system built over the decades to track the ships of potential enemies.
   Earth scientists announced at a news conference recently that they had used the system for closely monitoring a deep-sea volcanic eruption for the first time and that they plan similar studies.
   Other scientists have proposed to use the network for tracking ocean currents and measuring changes in ocean and global temperatures.
   The speed of sound in water is roughly one mile a second-slower than through land but faster than through air. What is most important, different layers of ocean water can act as channels for sounds, focusing them in the same way a stethoscope(听诊器) does when it carries faint noises from a patient’s chest to a doctor’s ear. This focusing is the main reason that even relatively weak sounds in the ocean, especially low-frequency ones, can often travel thousands of miles.
Which of the following is true about the U. S. Navy underwater listening network?
选项 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B、It has been replaced by a more advanced system.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.
答案A
解析 关于美国海军海底监听体系，文中第三段有明确说明的是这种技术现在部分地向民用研究科学家开放。
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