In some viruses, RNA is present instead of DNA indicating that

Correct Answer : D.

Viruses are defined as infectious nucleoproteins. A complete virus particle is called virion whose main function is to deliver its DNA or RNA gesnome into the host cell, so that genome can be expressed by the host cell. In a particular virus either DNA or RNA is genetic material, never both are present in a virus. Hence, viruses are:
(i) Double stranded DNA or ds DNA - Hepatitis B
(ii) Single stranded DNA or ss DNA - coliphage
(iii) Double stranded RNA or ds RNA - Reo virus, wound Tumor virus
(iv) Single stranded RNA or ss RNA - Tobacco mosaic virus (TMV)