Xiao Li was supposed __________ her homework before nine o'clock. But she couldn't.
A:to finish
B:to finishing
C:finish
D:finishing
如图所示,质量相同的两物体处于同一高度,A沿固定在地面上的光滑斜面下滑,B自由下落,最后到达同一水平面,则( )
这段短文的主要意思是( )
5+1=____
6-0=____
5+5=____
4+2=____
7-7=____