All viruses contain guanine in their genetic material

Steps:

• Viruses have either DNA or RNA as genetic material.
• DNA bases are adenine, thymine, guanine, cytosine.
• RNA bases are adenine, uracil, guanine, cytosine.
• Guanine is common to both DNA and RNA.

Why D is correct:

• Guanine is a purine base present in the nucleic acids of all viruses, as defined by the universal structure of DNA and RNA.

Why the others are wrong:

• A. Uracil replaces thymine only in RNA viruses, absent in DNA viruses.
• B. Ribose sugar is in RNA viruses; DNA viruses use deoxyribose.
• C. Thymine is specific to DNA viruses, replaced by uracil in RNA viruses.

Final answer: D