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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 (爆发) 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. (283 words)
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B、It has been replaced by a more advanced system.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 本题属于判断题，可以用排除法来解题。文中第三段说“冷战后，民用科学家能部分使用海军水下监听系统……”，选项A表达了这一意思，为正确答案。B“海军水下监听网络将被一种更高级的系统所取代”和D“海军水下监听网络在保护濒临灭绝的物种方面必不可少”是错误的，C的说法文中没有提到。
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