Answer: The correct option is C.
Cloning vectors.
Step-by-step explanation:
Viruses are use as cloning vectors because they can give the new gene or birth the new gene by infecting the cell. They are so modified and orogrammed in such a way that they cannot cause disease when it is used in humans. Cloning vector is a DNA fragment gotten from viruses or bacteria plasmid which is maintained and used for cloning purposes.