下列说法中正确的是:( )
A.一切波都能发生干涉和衍射现象
B.质点的振动方向与波的传播方向相互垂直的波是纵波
C.只有横波才能发生反射和折射现象
D.发生干涉的两列波频率一定相同
AD
产后15天阑尾位置为()妊娠12周阑尾位置为()妊娠40周阑尾位置为()
A.髂上2横指
B.髂下2横指
C.髂嵴水平
D.右髂前上棘至脐连线中外1/3处
E.胆囊区
Having become famous, Wang Baoqiang often has people ______ him in the street and ______ for his autograph (签名).
A.stopping, asking
B.stop, ask
C.stopping, to ask
D.to stop, asking