Two extremely long, parallel conducting cylinders, each of radius \(R\), are oriented parallel to each other with a center-to-center separation distance \(d\), where \(d \gg R\). The two cylinders carry uniform linear charge densities of \(+\lambda\) and \(-\lambda\), respectively. Which of the following expressions represents the capacitance per unit length \(C/L\) of this two-cylinder system?