苹果为什么会下落?因为有重力场。
电子为什么会做圆周运动?因为有磁场。
羽毛球为什么会在空中飞舞?因为有羽毛球场!
cxe LV 1
By signing up a HFOJ universal account, you can submit code and join discussions in all online judging services provided by us.
Using your HFOJ universal account