Certain viruses are instrumental in converting proto-oncogenes to oncogenes. This conversion most commonly results because:

A) viruses specifically infect cells that contain proto-oncogenes.
B) only viruses contain genes that can convert proto-oncogenes into oncogenes.
C) the proto-oncogenes are more likely to undergo mutation or recombination within a virus.
D) viruses contain the remainder part of the DNA that is added to the proto-oncogene to form the oncogene.