A solid insulating sphere of radius \(R\) is centered at the origin and has a non-uniform volume charge density given by \(\rho(r) = C r\) for \(r \le R\), where \(C\) is a positive constant and \(r\) is the radial distance from the center. Outside the sphere (\(r > R\)), the charge density is zero. Which of the following graphs best represents the electric flux \(\Phi_E\) through a concentric spherical Gaussian surface as a function of its radius \(r\)?