Two wires of resistivity $\rho 1$ and $\rho 2$ are connected in series. Equivalent resistivity of the combination is

Question

$\begin {array} {1 1} (A)\;\rho_1+\rho_2 & \quad (B)\;\large\frac{1}{2} (\rho_1+\rho_2) \\ (C)\;2\large\frac{\rho_1\rho_2}{\rho_1+\rho_2} & \quad (D)\;\large\frac{1}{2}\large\frac{\rho_1\rho_2}{\rho_1+\rho_2} \end {array}$