This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nucleotides, Subject name: Biochemistry
Which of the following DOES NOT contribute to the ring of thymine ? 
Select and explain. 
A. Aspaate, B. Glutamine, C. THF, D. Bicarbonate
C: THF
Answer: C: THF 
Explanation: The question asked specifically about the ring and not side groups present on ring. In Thymine (Pyrimidine) ring, sources of N & C are: N3 from Glutamine C2 from CO2 (or Bicarbonate) N1, C4, C5, C6 from Aspaate -CH3 is not pa of the ring but a side group which is contributed by THF, Hence it is the answer.