用测力计两次拉着重为G的物体竖直向上运动,两次运动的s-t图象,如图所示,其对应的测力计示数分别为F1,F2,则F1和F2的关系是( )
A:F1>F2
B:F1=F2
C:F1<F2
D:以上三种情况都有可能
I ate a hamburger this morning.
My sister likes singing, but she can't sing _____.