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

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.

different numbers of chromosomes

the answer would most likely be c, because if it's a comical piece of information, it may likely not be true, if it's a site that allows anybody to edit the content, it could mean a five year old is typing the info, and if it's a tv show produced by a celeb, it may have a biased opinion.