The correct statements regarding Ellingham's diagram are

below 710^oC, CO is a more effective reducing agent than carbon

it gives a clear explanation of need for the conversion of metal sulphide to corresponding oxides before reduction

metal oxides have less negative value of $∆{\mathrm{G}}^{\mathrm{o}}$as compared to CO₂ hence, oxidation of metal sulphides to oxides is not favourable

a metal can reduce the oxide of only those metal which lies above it in the Ellingham diagram