Gun control is a subject Americans have argued for a long time. A. of which B. with which C. about which D. into which 答案:C 考查定语从句,先行词是Gun control,指物,关系词在从句中做介词的宾语,介词前置,介词与从句动词构成搭配argue about sth.,选C。 如图所示,质量为M的斜劈形物体放在水平地面上,质量为m的粗糙物块以某一初速度沿劈的斜面向上滑,至速度为零后又加速返回,而物体M始终保持静止,则在物块m上、下滑动的整个过程中( )A.地面对物体M的摩擦力先向左后向右B.地面对物体M的摩擦力方向没有改变C.地面对物体M的支持力总大于(M+m)gD.物块m上、下滑动时的加速度大小相同