声波可以用来传递信息和能量，下列事例中属于利用声波传递能量的是（ ）
A．播放歌曲
B．教师讲课
C．超声波洁牙
D．敲打西瓜鉴别生熟
A、播放歌曲，是告诉我们播放的是哪一首歌，是声音传递信息．
B、教师讲课，是告诉我们知识，是声音传递信息．
C、超声波洁牙，是去掉牙齿上的牙垢，改变了牙齿，是声音传递能量．
D、敲打西瓜鉴别生熟，是通过敲打，让声音告诉我们西瓜生熟，是声音传递信息．
故选C．
It was unusually quiet in the emergency room on December 25. I was the nurse on duty that day. I didn't think there would be any patients. Just then five bodies 1 at my desk, a pale woman and four small children. “Are you all sick?” I asked. “Yes,” she said 2 , lowering her head. But when they described their problems, things got a little strange. Two of the children had headaches, but they didn’t show any 3 of headaches at all. Two children had earaches, but only one could tell me which ear was affected. The mother 4 of a cough but seemed to work to produce it. I didn't say anything, 5 I explained that they might wait for a little while before a doctor saw her. She answered, “Take your time; it's warm here.” I checked the chart after another nurse had finished registering(登记) the family. No 6 —they were homeless. The waiting room was warm. I looked at the family by the Christmas tree. The littlest one was pointing at the television and saying something to her mother. The oldest one was looking at lights on the Christmas tree. I went back to the nurses' station and mentioned we had a homeless family in the waiting room. The nurses who felt bored with 7 Christmas, turned to compassion((怜悯) for the family just trying to get warm on Christmas. The team went into action. We began to prepare a party for our Christmas 8 . We needed presents. We put together oranges and apples in a basket. We collected from different departments candies, crayons and other things available that could be presents. 9 , as the family walked to the door to leave, the four-year-old child came running back, gave me a hug and 10 , “Thanks for being our angels today.”
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