101.A solid, uncharged conducting sphere of radius 3a contains a hollowed spherical region of radius a. A point charge +Q is placed at the common center of the spheres. Taking V=0 as r approaches infinity, the potential at position r=2a from the center of the spheres is:
(A) 0
(B) 3a2kQ
(C) 3akQ
(D) akQ