A:Beside
B:Except
C:Apart from
D:But
a、b两种单色光组成的光束从介质进入空气时,其折射光束如图所示。用a、b两束光( )
He is kind to me. He always ____ ____ ____ me with the problems in my study.
一物体受到同一直线上两个力的作用,F1=200牛,F2=300牛,则此二力合力的大小可能等于( )