—Do you regret paying twenty dollars for the dictionary?

—No．I ____ twice as much for it．

A．gladly paid

B．should gladly pay

C．would gladly have paid

D．had gladly paid

如图所示，质量为m₀的斜劈放在水平地面上，质量为m的粗糙物块以某一初速度沿斜劈的粗糙斜面向上滑，速度为零后又加速返回，而斜劈始终保持静止，则在物块上下滑动的整个过程中

A．地面对斜劈的摩擦力先向左后向右

B．地面对斜劈的摩擦力方向没有改变

C．地面对斜劈的支持力总小于(m₀＋m)g

D．地面对斜劈的摩擦力大小不同