The physical properties of three substances, R, S and T, are given below. R: $mp = 801^\f$, $bp = 1413^\f$, electrical conductivity in the solid state: poor S: $mp = 2852^\f$, $bp = 3600^\f$, electrical conductivity in the solid state: poor T: $mp = 3550^\f$, $bp = 4827^\f$, electrical conductivity in the solid state: good Which substances could R, S and T be?
- AR: MgO, S: NaCl, T: C (graphite)
- BR: MgO, S: NaCl, T: $\text{SiO}_2$
- CR: NaCl, S: MgO, T: C (graphite)
- DR: NaCl, S: MgO, T: $\text{SiO}_2$