Which of the following bases are classified as purines?

Purines are one of the two types of nitrogenous bases found in nucleic acids, with the other type being pyrimidines. The two main purine bases in DNA and RNA are adenine (A) and guanine (G).

In the context of this question, the classification of the bases pertains specifically to their structural characteristics. Purines are characterized by a double-ring structure, which is distinct from the single-ring structure of pyrimidines like cytosine (C), thymine (T), and uracil (U) in RNA.

Therefore, identifying adenine and guanine as the purine bases leads to the conclusion that the correct identification of purines is accurately reflected in the chosen answer, as it correctly states that adenine and guanine are the bases classified as purines.