A charge Q is distributed over two concentric hollow spheres of radii r and R(R>r) such that the surface densities are equal. The potential at the common center is \[\frac{1}{4\pi {{\varepsilon }_{0}}}\]times-

• A. \[Q\left[ \frac{r+R}{{{r}^{2}}+{{R}^{2}}} \right]\]                 
• B. \[\frac{Q}{2}\left[ \frac{r+R}{{{r}^{2}}+{{R}^{2}}} \right]\]
• C. \[2Q\left[ \frac{r+R}{{{r}^{2}}+{{R}^{2}}} \right]\]   
• D. zero