Combining Multiple Text Lists into One Text list Field

I have three text lists as input:

List A = [A, B, C]

List B = [E, F]

List C = [G, H]

I want to combine these into a single text list as output, like this:[A, B, C, D, E, F, G, H]

The output field is of type formula-multiselect. Could anyone please suggest the best way to combine these lists within a QuickBase formula?