Why Is Cryolite, Na₃AlF₆, Mixed with Aluminum Oxide Prior to Electrolysis

Why is cryolite, Na₃AlF₆, mixed with aluminum oxide prior to electrolysis to produce Al?

A) because sodium is produced which in turn displaces the aluminum.
B) the aluminum in cryolite is easier to reduce than that in aluminum oxide.
C) to provide more fluoride ions.
D) to reduce the temperature required to melt the aluminum oxide.
E) to shift the equilibrium to the right.