Which statement best describes the electric field produced by an isolated conducting sphere carrying a net positive charge +Q?
a) The electric field has the same constant magnitude kQ/R2 everywhere both inside and outside the sphere.
b) The field is zero everywhere inside the sphere and, beyond the surface, behaves identically to that of a point charge +Q located at the center.
c) Inside the sphere the field decreases linearly with distance from the center, and outside the field obeys E=kQ/r2.
d) The field is zero throughout the interior, but outside the sphere it decreases with distance as E=kQ/r3.