Which nitrogenous base category contains thymine?

Thymine is classified as a pyrimidine, which is one of the two categories of nitrogenous bases found in nucleic acids. Pyrimidines are characterized by their single-ring structure, and they include thymine, cytosine, and uracil. In contrast, purines, such as adenine and guanine, have a two-ring structure. Since thymine specifically belongs to the pyrimidine category, the correct answer reflects its classification as a pyrimidine, distinguishing it from purines and ensuring clarity on the structural differences between these two types of nitrogenous bases.