Final answer:
The correct answer, which includes all of the pyrimidines found in both RNA and DNA, is B) cytosine, uracil, and thymine. Thymine is exclusive to DNA, and uracil is unique to RNA, with cytosine being found in both.
Step-by-step explanation:
The pyrimidines found in both RNA and DNA are cytosine, thymine, and uracil. Thymine is found only in DNA, while uracil is specific to RNA. Cytosine is common to both. Within the structures of DNA and RNA, the nitrogenous bases play a critical role. DNA contains four nitrogen bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In contrast, RNA comprises adenine (A), guanine (G), cytosine (C), and uracil (U). Adenine and guanine are classified as purines, which are characterized by their double-ring structure.
Cytosine, thymine, and uracil, on the other hand, are pyrimidines, which feature a single ring in their structure. To remember the pyrimidines, one can use the mnemonic 'cut pyramid', where 'c' stands for cytosine, 'u' for uracil, 't' for thymine, and 'pyramid' denotes pyrimidines. Since the question asks about the pyrimidines in both RNA and DNA, the correct answer must include cytosine, uracil, and thymine, as these encompass the pyrimidines present in both nucleic acids.