P is a point at a distance r from the centre of a solid sphere of radius R0. The gravitational potential at P is V. If V is plotted as a function of r, then the curve representing the plot correctly is

$V=\left\{\begin{array}{l}-\frac{G M}{r} \quad~~, ~~\quad~~\quad r \geq R_0 \\ -\frac{G M}{2 R_0^3}\left(3 R_0^2-r^2\right), r<R\end{array}\right.$