The answer to this question is 'd'
Viruses cannot reproduce independently.
Unlike normal animal or plant cells they lack cellular systems needed for reproduction. Due to this,one of the five major characteristics that distinguish viruses from other living things is that they cannot undergo binary fission.
Why do they lack cellular systems?
They do not have cellular systems for the simple reason that they lack the
genetic information for synthesis of these systems. The genetic information they carry in their nucleic acids (DNA or RNA) is limited for production of their own viral components or "body parts" and these parts are capsid, nucleic acids and envelope (for enveloped viruses).
They therefore depend 100% on the cellular mechanisms of other organisms to be able to reproduce and must invade them and sequester or commandeer the already formed systems of their host for this purpose. Thus viruses are called obligate parasites.
