An infinitely long, solid nonconducting cylinder of radius \(R\) has a nonuniform volume charge density given by \(\rho(r) = \rho_0 \left(1 - \dfrac{r}{R}\right)\) for \(r \le R\), where \(r\) is the radial distance from the central axis and \(\rho_0\) is a positive constant. Which of the following integral expressions correctly gives the magnitude of the electric field \(E(r)\) at a distance \(r < R\) from the central axis?