"Then what "race" are Arabs, Native Americans, Aborigines, etc., etc., etc.: white, black or Asian?"
These are mixtures of varying amounts and degrees of the three primary races. Some people might also call them mongrels. This is an out-dated and derogatory term, which is nevertheless very accurate. Also, the Germans are most definitely not the same as the Chinese or even the Italians.
Yes, I learned that there are three primary races when I was a child. This is what I will always believe in. And I don't blindly believe in what I was told, either. I observe things when my own eyes and the conclusion that I have reached is that indeed there are these three primary races.