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
Number of ATP required for synthesis of 1 mole of urea is: 
Select and explain. 
A. 3, B. 4, C. 6, D. 12
A: 3
Answer: A: 3 
Explanation: Synthesis of 1 mol of urea requires 3 mol of ATP plus 1 mol each of ammonium ion and of the a-amino nitrogen of aspaate. Ref: Harper 28th edition, chapter 28.