If chimpanzees and human genomes differ only about 1.3 at the level of DNA base pairs, then how can ...

If chimpanzees and human genomes differ only about 1.3 at the level of DNA base pairs, then how can we explain the dramatic differences in appearance, behavior, cultures, etc., between humans and chimps?
 
  a. There is a correlation between increased rates of divergence with known functions of alleles in humans and chimps.
  b. Natural selection has been acting on clusters of genes associated with both survival and repro-duction in humans and chimps.
  c. Important differences exist in the expression of genes in humans and chimps.
  d. Two of the above can explain the differences.