下列与原文完全一致的一项是[ ]
A.潇潇暮雨杜鹃啼。
B.谁道人生无再少?门前流水亦向西!
C.水是眼波横,山是眉峰聚。
D.才将送春归,又送君归去。
答案:C
一简谐横波在x轴上传播,波源振动周期T=0.1s,在某一时刻的波形如图所示,且此时a点向下运动.则( )
A.波速为20m/s,波沿x轴正向传播
B.波速为10m/s,波沿x轴负向传播
C.波速为20m/s,波沿x轴负向传播
D.波速为10m/s,波沿x轴正向传播
I could have helped the old man ______ yesterday morning.
A.did I come
B.if I came
C.had I come
D.if I should come