The correct option is A DNA has no role in life cycle.
Retroviruses are single-stranded RNA virus belongs to the family retroviridae. Retrovirus carry the genes for reverse transcriptase enzyme which is a RNA dependent DNA polymerase. This enzyme uses RNA as a primer to synthesise cDNA which is then incorporated into the host genome. The host cell then treats the viral DNA as part of its own genome, transcribes and translates the viral genes along with the cell's own genes producing the proteins required to assemble new copies of the virus. This explains the important role of DNA in life cycle. Retroviruses cause tumour growth and certain cancers in animals. So the correct answer is 'DNA has no role in life cycle'.