In which one of the following ways does a proto-oncogene differ from an oncogene?

A) Proto-oncogenes code for proteins that regulate the expression of structural genes; oncogenes code for nucleic acids involved in cell division.
B) Proto-oncogenes control normal cell division; oncogenes contribute to the development of cancer.
C) When oncogenes become damaged, they become proto-oncogenes.
D) Oncogenes activate tumor suppressor genes; proto-oncogenes repress tumor suppressor genes.
E) Proto-oncogenes cause cells to self-destruct when damaged; oncogenes cause damaged cells to repair themselves.