Which of the following statements correctly describes the structural difference between purines and pyrimidines?

• A. Purines have two rings, while pyrimidines have one ring.
• B. Purines have one ring, while pyrimidines have two rings.
• C. Both purines and pyrimidines have two rings.
• D. Purines and pyrimidines have the same ring structure.

Answer: (A)