质量为m的小球在竖直面内的光滑园轨道上做圆周运动，园的半径为R,小球经过园环最高点时刚好不脱离圆环，则其过最高点时，下列说法正确的是 （ ）                          

A．小球对圆环的压力大小等于mg ;

B．小球受到的合外力大小等于mg ；

C．小球的线速度大小为0；

D．小球的加速度大小为g .

At the end of the closing process group, （）.

A．it is verified that the defined processes are completed within all the process groups to close the project phase

B．it is determined that the product of the project is completed satisfactorily

C．project management plan is written off by the project sponsor

D．new change requests are initiated as required