题干
Don't do any other things while you are doing your homework. So please _________ your MP3.
A：turn up
B：turn down
C：turn on
D：turn off
答案(点此获取答案解析）
D
Don't do any other things while you are doing your homework. So please _________ your MP3.
A：turn up
B：turn down
C：turn on
D：turn off
轴传播，下左图是波上某一质点
的振动图线。下右图为这列横波在0.1s时刻的波形图。由此可以判断该波的传播速度和传播方向是