A phosphorescent red strain of bacteria is heat-killed and mixed with a living, colorless strain. Further observations of the mixture show that some of the living cells are now red. Which of the following observations would provide the best evidence that red color is a heritable trait?

A) especially bright red color in some members of the living strain
B) as the living cells divide the number of red cells increases
C) when the heat-killed and living cells are mixed there is a decrease in the overall amount of red color
D) after a few generations there are no more colorless cells, all cells are red