Question: pyrimidines have how many rings?
Answer: The pyrimidines, cytosine and uracil, are smaller and have a single ring, while the purines, adenine and guanine, are larger and have two rings. C. The purines, adenine and guanine, are larger and have two a one-ringed structure, while the pyrimidines, thymine and cytosine, have two rings and are smaller.