The correct options are
C aluminium from Al2O3
D magnesium from CaCO3.MgCO3
Look for reactive metals. Another clue would be to keep your eyes peeled for compounds
that do not melt easily. Alternatively, think in terms of Ellingham diagram - as in oxides
that would be extremely hard to reduce with carbon.
aluminium is extracted by the Hall-Heroult process where Al2O3 is mixed with fluorspar
and cryolite and then subjected to fused electrolysis (non-aqueous).
Likewise, Mg is obtained from fused salt electrolysis of MgCl2