question: Q:Except for identical twins, no two people are genetically identical. Which of the following statements most accurately describes the main source of variation in humans?? 
  A:The main source of variation in humans is genetic drift.;B:Changes in the environment cause rapid changes in different human populations.;C:Shuffling of alleles is responsible for the greatest variation in humans.;D:Mutations are responsible for the greatest changes in different human populations.