61. The nonconducting hollow sphere of radius R shown above carries a large charge +Q , which is uniformly distributed on its surface. There is a small hole in the sphere. A small charge +q is initially located at point P. a distance r from the center of the sphere. If k=1/4πεo, what is the work that must be done by an external agent in moving the charge +q from P through the hole to the center O of the sphere?
(A) kqQ/r
(B) kqQ/R
(C) kq(Q−q)/r
(D) kqQ(1/R−1/r)