遇到巨大声响时，要迅速张开嘴，或闭嘴堵耳，这种做法主要是为了
A．保护耳蜗内的听觉感受器
B．保持鼓膜内外气压平衡
C．使咽鼓管张开，保护听小骨
D．防止听觉中枢受损伤
答案：B
题目分析：当听到巨大声响时，空气震动剧烈导致鼓膜受到的压力突然增大，容易击穿鼓膜．这时张大嘴巴，可以使咽鼓管张开，因咽鼓管连通咽部和鼓室．这样口腔内的气压即鼓室内的气压与鼓膜外即外耳道的气压保持平衡．保持鼓膜内外大气压的平衡，以免振破鼓膜．如果闭嘴同时用双手堵耳也是同样道理，这样就避免了压强的突然改变，对鼓膜的影响．
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| I first had physics lessons when I was in Grade Eight some years ago. In class, I 1 that there wasn't a Nobel (诺贝尔) Prize winner from China. That made me sad, and I decided to change (改变) it. 2 after that, I got up early in the morning. I turned on the light and took out a physics book. Then I started 3 quietly. I worked so hard because I had a great 4 - one day, I would be the first 5 person to win the Nobel Prize in physics. Later on, I found physics at school too easy for me. I wanted to lean 6 , so I made a reading plan and started to find answers to more difficult problems. Now I am a top student in physics. I won the first prize in the national physics competition last monh. And I am happy to be closer to my dream after a few 7 hard work. Of course, 8 I have some problems. My classmates always 9 me when they are talking about fashion (时尚) or pop stars, because I know 10 about them. "Well, that doesn't matter too much," I tell myself. "They don't know much about physics , but I won't laugh at them." | ||
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