单项选择题
A.波长为0.5m B.波长为0.05m C.波速为25m/s D.波速为5m/s
A.0.5 B.0.7 C.1 D.0.9
A.x+y-3z-6=0 B.2x+5y-z+2=0 C.x-y+5z+7=0 D.x-y+5z-22=0