Proto-oncogenes can change into oncogenes that cause cancer.Which of the following best explains the presence of these potential time bombs in eukaryotic cells?

A)Proto-oncogenes first arose from viral infections.
B)Proto-oncogenes normally help regulate cell division.
C)Proto-oncogenes are genetic "junk."
D)Proto-oncogenes are mutant versions of normal genes.
E)Cells produce proto-oncogenes as they age.