波后
参考答案：
某一时刻介质中各点的振动刚好停止，这一曲面叫波后，也叫波尾。
There is no point arguing about what _____ the accident, I’d rather you _____ the victims of it.
A．led to; focus on
B．led to; focused on
C．caused ; focus to
D．caused to, focused to
我国专门针对境内哪条河流制订有采沙管理办法？（）
A.黄河
B.长江
C.淮河
D.钱塘江
