5. Which of the following is true about the U.S. Navy underwater listening network?

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B) It has been replaced by a more advanced system.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.

Passage 3

Dogs are social animals and without proper training, they will behave like wild animals. They will spoil your house, destroy your belongings, bark excessively, fight other dogs and even bite you. Nearly all behavior problems are perfectly normal dog activities that occur at the wrong time or place or are directed at the wrong thing. The key to preventing or treating behavior problems is learning to teach the dog to redirect its normal behavior to outlets that are acceptable in the domestic setting.

One of the best things you can do for your dog and yourself is to obedience train (驯服) it. Obedience training doesn't solve all behavior problems, but it is the foundation for solving just about any problem. Training opens up a line of communication between you and your dog. Effective communication is necessary to instruct your dog about what you want it to do.

Training is also an easy way to establish the social rank order. When your dog obeys a simple request of “come here, sit,” it is showing obedience and respect for you. It is not necessary to establish yourself as top dog or leader of the dog pack (群) by using extreme measures. You can teach your dog its subordinate (从属的) role by teaching it to show submission to you. Most dogs love performing tricks for you to pleasantly accept that you are in charge.

Training should be fun and rewarding for you and your dog. It can enrich your relationship and make living together more enjoyable. A well-trained dog is more confident and can more safely be allowed a greater amount of freedom than an untrained animal.

5. The present situation in about half of the states is that the graduated licensing system ________.

A) is under discussion          B) is about to be set up

C) has been put into effect    D) has been perfected

Passage 2

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.

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