$\begin{array}{1 1} \text{$R_1$ and $R_2$ in series and the resultant in parallel with $R_3$} \\ \text{$R_1$ and $R_3$ in series and the resultant in parallel with $R_2$} \\ \text{$R_2$ and $R_3$ in parallel and the resultant series in with $R_1$} \\ \text{$R_1$ and $R_2$ in parallel and the resultant series with $R_3$} \end{array} $