The answer is E; Self-interest study. This is due to the fact that the financier of the research, the beverage company, has vested interests in the research and will therefore be intuitively biased for the results to favour the sales of the beverage.
(In most cases) A child from red+black haired parents would have black hair. The allele for black hair is dominant to that of red, and would be the phenotype of the hair.
