This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Proteins and Amino Acids, Subject name: Biochemistry
Nitrogen atoms of Urea contributed by: 
Select and explain. 
A. Ammonium and aspartate, B. Ammonium and glutamate, C. Ammonium and glycine, D. Ammonium and asparagine
A: Ammonium and aspartate
Answer: A: Ammonium and aspartate 
Explanation: Ans. A. Ammonium and aspartateFirst nitrogen by Ammonium ion--by the reaction CPS-1Second nitrogen by Aspartate--by the reaction Argininosuccinate Synthetase