Which of the following bases are classified as pyrimidines?

Pyrimidines are a class of nitrogenous bases characterized by a single six-membered ring structure. In the context of nucleic acids, the pyrimidines include cytosine, thymine, and uracil. These bases play crucial roles in the structure and function of DNA and RNA.

Cytosine is used in both DNA and RNA, while thymine is specific to DNA and uracil replaces thymine in RNA. The defining feature of pyrimidines is their simpler structure compared to purines, which consist of a fused double-ring system.

The option identifying cytosine, thymine, and uracil correctly classifies all three as pyrimidines, reinforcing their importance in genetic coding and nucleotide pairing. This understanding of pyrimidines is fundamental in molecular biology, genetics, and biochemistry, as these bases are integral to DNA and RNA structure.