— How many ________ were on the bus when the accident happened?
— About forty. Seven of them were kids.
A:animals
B:machines
C:letters
D:Passengers
如图所示,弹簧所受重力不计,上端固定在天花板上,下端挂一个 小球,处于静止状态。下列各组力中属于平衡力的是( )
“食客”准备着
自然界中氧气主要来自于( )