Deduced from the following values of half cells, what combination of two half cells would result in — Electrochemistry Chemistry Question

Question

Deduced from the following $E^\circ$ values of half cells, what combination of two half cells would result in a galvanic cell with the largest positive standard cell potential? (i) $A^{3-} \rightarrow A^{2-} + e^-$, $E^\circ = 1.5\text{ V}$; (ii) $B^{2+} + e^- \rightarrow B^+$, $E^\circ = 2.1\text{ V}$; (iii) $C^{2+} + e^- \rightarrow C^+$, $E^\circ = +0.5\text{ V}$; (iv) $D \rightarrow D^{2+} + 2e^-$, $E^\circ = -1.5\text{ V}$. Note: The potentials given are strictly for the reactions exactly as written.