A:So what
B:Why not
C:How come
D:What if
—Can I have a day off tomorrow, Mr. Johnson?
—________. I can manage without you.
用如图所示的四种机械提起同一重物,不计机械自重和摩擦,最省力的是( )
则△OCD与四边形ABDC的面积比为( )