In a theoretical model of a screened electrostatic interaction, the electric potential in a region of space with spherical symmetry is given by the function \(V(r) = \dfrac{C}{r} e^{-r/a}\), where \(C\) and \(a\) are positive constants and \(r\) is the radial distance from the origin (\(r > 0\)). Which of the following expressions represents the radial component of the electric field, \(E_r(r)\), as a function of \(r\)?