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【多选题】
关于超声波的物理概念，下列哪些是正确的（ ）A.
超声波属机械波
B.
超声波的频率在20kHz以上
C.
医用诊断用超声的频率一般在1MHz以上
D.
超声波有纵波、横波、表面波等3种
E.
医用诊断用超声波的纵波
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