Miss Chen said Lao She was famous _______his play Teahouse.
A:about
B:at
C:for
D:as
70+24=____ 81-5=____ 9+36=____
50-8=____ 75-15=____ 72-6=____
98-20=____ 7+33=____ 56-9=____
质量为m的物体从静止开始自由下落,不计空气阻力,在t时刻重力对物体做功的功率是( )