Haematite containing silica as the main gangue is smelted with limestone. The flux that actually acts on the gangue, and the slag formed, are respectively

1. A$\mathrm{CaO}$ and $\mathrm{FeSiO}{}_3$
2. B$\mathrm{SiO}{}_2$ and $\mathrm{CaSiO}{}_3$
3. C$\mathrm{CaO}$ and $\mathrm{CaSiO}{}_3$
4. D$\mathrm{CaCO}{}_3$ and $\mathrm{CaSiO}{}_3$