The following are a set of node-voltage equations; draw the circuit they represent.

\[
\begin{aligned}
v_{\mathrm{A}} & =v_{\mathrm{S}} \\
\frac{v_{\mathrm{B}}-v_{\mathrm{A}}}{R_{1}}+\frac{v_{\mathrm{B}}-v_{\mathrm{C}}}{R_{2}}-i_{\mathrm{S}} & =0 \\
\frac{v_{\mathrm{C}}-v_{\mathrm{A}}}{R_{3}}+\frac{v_{\mathrm{C}}-v_{\mathrm{B}}}{R_{2}}+\frac{v_{\mathrm{C}}}{R_{4}} & =0 \\
v_{\mathrm{D}} & =0
\end{aligned}
\]