What do pyrimidines include?

Pyrimidines are a category of nitrogenous bases that are essential components of nucleotides, which make up nucleic acids like DNA and RNA. The two primary pyrimidines found in DNA are cytosine and thymine. In the context of RNA, an additional pyrimidine, uracil, replaces thymine. Therefore, both cytosine and thymine can be classified as pyrimidines, as well as uracil.

By recognizing that options mentioning these bases—specifically cytosine, thymine, and uracil—aligns with the definition of pyrimidines, it becomes clear why the inclusion of choices B (Cytosine and Thymine) and C (Thymine and Uracil) together supports the overall categorization. Therefore, collectively choosing both sets of bases, as represented in the combined choice, accurately reflects the classification of pyrimidines in nucleic acids.