单项选择题
A.四/4h/10mi nB.六/6h/10mi nC.四/4h/15mi nD.六/6h/15mi n
A.①②④⑥B.①②⑤⑥C.①③④⑤D.②③⑤⑥
A.感应电动势B.水压力C.多普勒频移D.相关延时