A:三种情况下物体损失的机械能△E3>△E2>△E1
B:三种情况下摩擦产生的热量Q1=Q2<Q3
C:物体滑到底端时的速度v1>v2=v3
D:物体运动到斜面底端时的时间t1<t2<t3
The teacher did what she could _____ that child.
This math problem isn't so difficult that I can work it out .
you smile at others,they will smile back.