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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

admin2010-01-15  92
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 does when it carries faint noise from a patient’ s chest to a doctor’ s ear. This focusing is the main reason why even relatively weak sounds in the ocean, especially low-frequency ones, can often travel thou- sands of miles.
The deep-sea listening system makes use of ______.
选项 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
答案C
解析 文章的最后一段讲述“the deep-sea listening system"的工作原理，其中讲到“What is most important，different layers of ocean water can act as channels for sounds…”，由此可见，这一系统就是利用了在传送声音方面"layers of ocean water"的独特特性，因此，C 是正确答案。
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