This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Metabolism of nucleic acids, Subject name: Biochemistry
The following is an example for unusual base 
Select and explain. 
A. Di hydro uracil, B. Adenine, C. Cytosine, D. Uracil
A: Di hydro uracil
Answer: A: Di hydro uracil 
Explanation: It is present in tRNAPresent in the DHU OR D arm of tRNAServe as the recognition site for the enzyme which adds the amino acidRef: DM Vasudevan, 7th edition, page no: 597