Which flat do you live ________ and which floor do you live ________? A. in; on B. on; in C. in; / D. /; on 答案:A一简谐横波在x轴上传播,波源振动周期T=0.1 s,在某一时刻的波形如图11-1所示,且此时a点向下运动,则( ) 图11-1 A.波速为20 m/s,波向x轴正方向传播 B.波速为10 m/s,波向x轴负方向传播 C.波速为20 m/s,波向x轴负方向传播 D.波速为10 m/s,波向x轴正方向传播