Which statements about the extraction of zinc are correct?

1. Azinc is collected as a liquid at the bottom of the retort, since it is denser than the slag
2. Bthe sulphide is converted to oxide before reduction because carbon reduces the oxide more readily
3. Cthe ore is concentrated by froth flotation and then roasted to the oxide
4. Dreduction of ZnO with coke is carried out near $1673\mathrm{K}$ and zinc distils over as vapour