A solid, uncharged conducting sphere of outer radius \(R_2\) is centered at the origin \(O\) and contains an off-center spherical cavity of radius \(R_1\) whose center is displaced by a distance \(d\) along the \(x\)-axis from \(O\), where \(d + R_1 < R_2\). A point charge \(+Q\) is fixed at the center of the cavity. Assuming the electric potential is zero at infinity, which of the following is the correct expression for the electric potential \(V\) at a point inside the cavity at a distance \(r_1\) from the charge, where \(r_1 < R_1\)?