A solid insulating sphere has a uniform charge density $\rho$ throughout its volume. A spherical cavity is cut out of it, as shown in the figure. The centre of the cavity is at a distance $d$ from the centre of the sphere, and the cavity is entirely inside the sphere. The electric field inside the cavity is

Fig. 1: A uniformly charged sphere of charge density rho with centre O, and a spherical cavity inside it with centre O prime. The vector d runs from O to O prime.