A:hm
B:mh
C:hm
D:h+m
已知S是边长为1的正三角形ABC所在平面外一点,且SA=SB=SC=1,M,N分别是AB,SC的中点,则异面直线SM与BN所成角的余弦值为( )
Good table manners
We are going to hold a talk on good table manner. The purpose of the talk is to teach students