purines are double ringed nitrogenous bases of DNA and RNA including adenine and guanine. the three others are cytosine and thymine( uracil is present instead of thymine in RNA) are pyrimidines. So your answer should be (B) Improve Answer Solution purines are double ringed nitrogenous bases of DNA and RNA including adenine and guanine. the three others are cytosine and thymine( uracil is present instead of thymine in RNA) are pyrimidines. So your answer should be (B) Improve Answer.