一半径为R的均匀带电球面的带电量为q. 设无穷远处为电势零点，则球外距离球心为r的P点处的电场强

度的大小和电势为___ The charge of a uniformly charged sphere of radius R is q. suppose infinity is the zero of the electric potential, then the magnitude of the electric field intensity and the electric potential at point P with the distance from the outside of the sphere to the center of the sphere r are___

A、

B、

C、

D、