What causes the differences in physical characteristics like hair color among people? Different versions of genes variations in DNA length different numbers of chromosomes variations in cell nucleus size

Answer: First option, different versions of genes.

Explanation: Things like skin color, hair color, height and a lot of other things that you maybe can't see at plain sight (Like genetic diseases and such things) are totally determined by your genetics (which are passed from parents to their childs, and this is why they have similar traits), this means that the right answer is Different versions of genes.