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制作 TOFD 探头晶片的压电复合材料 PZT 陶瓷体积率增加,则: A.
探头晶片品质因数 Q 值增大,声阻抗增大 B.
探头晶片品质因数Q值增大,声阻抗减小 C.
探头晶片品质因数Q值减小,声阻抗增大 D.
探头晶片品质因数Q值减小,声阻抗减小

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A、
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C、
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可以减小混凝土收缩的措施是( )。
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单项选择题
Sometimes I feel that being the mother of three small children is like operating a large circus(马戏团).（21）afternoon last week, my three sons playing peacefully in the back yard(院子),（22）the ball from one to another. I jumped at the chance to talk to one of my friends（23）the phone, but before I（24）to the phone, I could tell the boys had begun to quarrel with each other about something. I rushed out to（25）peace, but before I got there Charles had（26）a rock at Mark, and hit him in the eye. By the time I got to the back yard, they had begun to（27）about this. Even David, the oldest boy, who won′ t usually fight with anybody about（28）, was involved(卷入,). First, I（29）them stop fighting, and then I examined Mark′ s eye. I decided that it wasn′t going to develop into a black eye, but I felt that they should（30）at least a little for（31）they had done "I′ m going to（32）to your father about this when he comes home for tomglat, said. "He and I will think of how to punish you. "Things were（33）quiet after that about half an hour, and then Charles（34）a glass in the kitchen, and at almost the same（35）, Mark fell out of the apple tree.
第（22）题选
A.catching
B.throwing
C.beating
D.playing
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