声音是由发声体的_______而产生的,在固体、液体和气体中,传播声的速度最慢的是________。
振动;空气
Jim often goes to school _____ bike. But today he goes to school _____ the school bus.
A.on, by
B.by, by
C.by, on
D.on, on
已知点A(20,8,8),与点A对称于W面的点B的坐标值是()
A.(20,-8,-8)
B.(-20,-8,8)
C.(-20,8,8)
D.(20,8,8)