D is the best of the options given. Alleles are different versions of a
gene. A given gene is localized (located) in a specific location on a
chromosome. A chromosome consists of genes. There are many different
versions of genes out there. (i.e. the gene for hair color could have an
allele coding for black, blond, red, brown, etc. colored hair. That
allele would be where you find the gene for hair color on the
chromosome.) Hope this helps! :)