单项选择题
A.2 B.2.19 C.0.5 D.28.6
A.π/2 B.π C.3π/4 D.3π/2
A.0.01cm B.0.01m C.-0.01m D.0.01mm
A.波速为C B.波长为2π/C C.周期为1/B D.圆频率为C
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