Which bases are classified as pyrimidines?

Pyrimidines are one of the two classes of nitrogenous bases found in nucleic acids. They are characterized by having a single six-membered ring structure. The specific bases classified as pyrimidines include thymine (T), uracil (U), and cytosine (C).

Thymine is found in DNA, while uracil is present in RNA, replacing thymine in this context. Cytosine can be found in both DNA and RNA. This distinction is important for understanding the structure and function of nucleic acids in biological systems.

The other bases in nucleic acids, such as adenine (A) and guanine (G), fall under the category of purines, which are characterized by a two-ring structure. By identifying the correct pyrimidine bases as thymine, uracil, and cytosine, it becomes clear why the selected answer fits the classification system used in molecular biology.