In a human, only the β cells of the pancreas make insulin and only the chief cells of the stomach make pepsinogen (an inactive form of the main digestive enzyme pepsin). This is most likely because:

a. Only the DNA of β cells contains the gene for insulin; only the DNA of chief cells contains the gene for pepsinogen
b. A different combination of control elements is found within enhancers associated with the insulin vs. pepsinogen genes
c. β cells and chief cells will synthesize the combination of activator proteins specific for the enhancers of the insulin and pepsinogen genes, respectively