A:is ; i
B:are; are
C: is; are
D:are; i
物理兴趣小组的同学利用如图所示装置,探究反射声音的强弱与充当反射面的材料是否有关。他们将发声的闹铃置于纸筒A内,将充当反射面的材料置于O处,通过纸筒B倾听反射的铃声强弱。
While ____ the dog, you were careless and it got ____ and was hit by a car.