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easy problem get noise high

Nature is wonderful.It is our best teacher.It teaches us a lot and we are born to learn from it to solve （1）______.For example,scientists used what they saw in nature to improve our way of travelling.In days of high- speed train research and development,scientists were once faced with a noise problem.The trains pushed air through tunnels at （2）______ speeds.So,when a train came out of a tunnel,it could be very,very （3）______.However,kingfisher birds hardly make a sound when they get into lakes or rivers.Engineers （4）______ a clever idea.They changed the front of the trains to match the shape of the kingfisher.Then the air could （5）______ pass over the trains.The problem was solved!