${\text{Al}}_2{\text{O}}_3$ can be converted to anhydrous ${\text{AlCl}}_3$ by heating :

1. A
   ${\text{Al}}_2{\text{O}}_3$ with $\text{HCl}$ gas
2. B
   ${\text{Al}}_2{\text{O}}_3$ with $\text{NaCl}$ in solid state
3. C
   a mixture of ${\text{Al}}_2{\text{O}}_3$ and carbon in dry ${\text{Cl}}_2$ gas
4. D
   ${\text{Al}}_2{\text{O}}_3$ with ${\text{Cl}}_2$ gas