$\begin{array}{1 1}(1) r_s=0.5 \Omega \text{n parallel with the galvanometer} \\ (2) r_s= 0.5 \Omega \text{in series with the galvanometer} \\ (3) r_s=1 \Omega \text{in series with galvanometer} \\ (4) r_s= 1 \Omega \text{in parallel with the galvanometer} \end{array} $