A:①③④
B:①②
C:②③
D:①②④
如图在光滑地面上,水平外力F拉动小车和木块一起作无相对滑动的加速运动.小车质量是M,木块质量是m,力大小是F,加速度大小是a,木块和小车之间动摩擦因数是μ,则在这个过程中,木块受到的摩擦力大小是( )
从方框中选词并用其适当形式填空
Many____like playing computer games after school. Rui Chenggang is a ____ from CCTV. Mrs Green likes writing ____for children.As a____ , he works late at night.During big festivals, the ____ are very busy.