Cytosine as a universal nucleotide base in genetic material

Steps:

• Viruses contain either DNA or RNA as genetic material.
• Prokaryotes and eukaryotes use DNA for their genomes.
• DNA bases are adenine, thymine, cytosine, and guanine.
• RNA bases are adenine, uracil, cytosine, and guanine, making cytosine common to all.

Why C is correct:

• Cytosine is a pyrimidine base found in the nucleotides of both DNA and RNA, the genetic material across viruses, prokaryotes, and eukaryotes.

Why the others are wrong:

• A: Ribose is the sugar in RNA only, absent in DNA of prokaryotes, eukaryotes, and DNA viruses.
• B: Deoxyribose is the sugar in DNA only, absent in RNA viruses.
• D: Thymine is a DNA-specific base, replaced by uracil in RNA viruses.

Final answer: C