Identify the correct statement with reference to the extractive metallurgy of aluminium ?

A. The electrolyte consists of molten Na3AlF6 with approximately 1 to 8% Al2O3
B. Approximately 80% of the aluminium deposited on the cathode comes from cryolite
C. Sodium is deposited along with aluminium, but is immediately vaporised
D. Anode effect sets in when the cryolite concentration goes below 40%.