单项选择题
A.几何尺寸B.磁特性C.磁感应强度D.磁场大小
A.dp=p0ds/λrsin(2πft+2πr/λ)B.dp=p0ds/λrcos(2πft-2πr/λ)C.dp=p0ds/λrcos(2πft+2πr/λ)D.dp=p0ds/λrsin(2πft-2πr/λ)
A.5mmB.5cmC.10mmD.2cm