answer is J K and Z

If you accept his silly notion that zero doesn't count. And the annoying fact that, although the K is eliminated on Latin grounds it is not eliminated on English grounds. Just because there is no K in any of the English roots does not mean that it could not, in theory, be there.

And as far as eliminating J for etymological reasons, if J is eliminated because it is a recent variation of I, then U is eliminated because it is a recent variation of V, so eliminating J on etymological grounds is invalid.