The four nitrogenous bases found in DNA are cytosine, thymine, adenine, and guanine. Which of the following statements regarding the bases is correct?

A) Adenine is a pyrimidine and pairs with cytosine in the DNA double helix.
B) Cytosine has a single ring structure and pairs with guanine in the DNA double helix.
C) Thymine is a purine and pairs with adenine in the DNA double helix.
D) Guanine has a double ring structure and pairs with thymine in the DNA double helix.