A:to learn, possible
B:of learning, possibly
C:of learning, was possible
D:to learning, possible
若方程x+y=3,x-y=1和x-2my=0有公共解,则m的取值为____ .
如图,点C为线段AB的中点,点D为线段AC的中点、已知AB=8,则BD=( )
分析如图所示的四个装置,结论正确的是( )