$\begin{array}{1 1} \text{a. $E =\frac{n e \rho}{V_d}$} \\ \text{b. $E = ne \rho V_d$} \\ \text{c. $E = \frac{n \rho V_d}{e}$ } \\ \text{d. $E=\frac{V_d}{ne \rho}$} \end{array}$
