A:Where was it
B:What was it
C:How was it
D:Why was it
在图中所示的简单机械中,忽略机械自重和摩擦,当提起相同重物时,最省力的是( )
若a﹣b=﹣3,则(a+1)2﹣b(2a﹣b)﹣2a=____