In the commercial electrochemical process for aluminium extraction,the electrolyte used is:

• A
  $Al(OH)_3$ in $NaOH$ solution
• B
  An aqueous solution of $Al_2(SO_4)_3$
• C
  $A$ molten mixture of $Al_2O_3, Na_3AlF_6$ and $CaF_2$
• D
  $A$ molten mixture of $AlO(OH)$ and $Al(OH)_3$