This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
Apart from occurring in nucleic acids, pyrimidines are also found in 
Select and explain. 
A. Theophylline, B. Theobromine, C. Flavin mononucleotide, D. Thiamine
D: Thiamine
Answer: D: Thiamine 
Explanation: Usually, purine and pyrimidine are found in nucleic acids (DNA and RNA) as a part of nucleotides.
Pyrimidines also occur in thiamine (vitamin B1) and alloxan.
Purine is also a structural component of a number of essential coenzymes, e.g. coenzyme-A, NAD+, NADP+ and FAD+.