某些电介质，当在其极化方向上施加电场时，该电介质会发生变形，这种现象称为“正压电效应”。
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电涡流式传感器可以进行位移、转速、振动等测量。（ ）
A. 对
B. 错
________is Christmas day.
A. Twenty-five of december
B. Twenty-fifth of December
C. The twenty-five of December
D. The twenty-fifth of December
English was taught at the beginnning of________century in China.
A. nineteen
B. nineteenth
C. the nineteenth
D. the nineteen
More than________ years ago, there was a war between these two cities.
A. three hundreds
B. three hundred
C. three hundred of
D. three hundreds of
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