A. spell books

　　B. magic wands

　　C. Hogwarts robes

　　D. sports equipment

　　31. For what purpose is the text written?

　　A. To tell a magic story.

　　B. To announce a new plan.

　　C. To introduce a theme park.

　　D. To offer a flying program.

　　D

　　In a little-known part of the counter-terrorism (反恐怖主义) world, one of the most effective detection systems is a 600-pound animal that works for about 20 pounds of fish a day.

　　Since the 1960s, the United States and a handful of other countries have trained dolphins and sea lions to detect sea mines and swimmers, and to recover worn-

　　-out torpedoes (鱼雷) and testing objects used in naval (海军的) exercises.

　　The U.S. Navy kept its Marine Mammal Program a secret until the 1990s, and this spring CNN became one of the first members of the media to witness firsthand how the program works.

　　The program trains about 75 Pacific bottlenose dolphins, with natural biosonar (生物声纳) that tracks better than any manmade device; and 35 California sea lions, with very good underwater eyesight.

　　Not only do these trained marine mammals track and save millions of dollars in U.S. military equipment, they are also helping to save lives. The Navy won’t reveal whether the dolphins and sea lions have effectively stopped terrorists attempting to do harm to the U.S.

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