题目

114. If you visited our school this month, you would be amazed to see a modern stadium ___ here.   A. is constructing                     B. were constructing             C. is being constructed          D. were being constructed 答案：C如图所示，小球m在竖直放置的光滑圆形管道内做圆周运动，下列说法中正确的有：BCBCA．小球通过最高点的最小速度为gRB．小球通过最高点的最小速度为零C．小球在水平线ab以下管道中运动时，外侧管壁对小球一定有作用力D．小球在水平线ab以上管道中运动时，内侧管壁对小球一定有作用力．