A:①②
B:③④
C:①④
D:②③
质量为m的物体以v0做平抛运动,经过时间t,下落的高度为h,速度大小为v,在这段时间内,该物体的动量变化量大小为( )
The allowance is only enough to________the most fundamental needs such as food and clothing.
△ABC中,∠B=1200,AC=7,AB=5,则cosC=( )