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
Sources of the nitrogen in urea cycle are the following: 
Select and explain. 
A. Aspaate and ammonia, B. Glutamate and ammonia, C. Arginine and ammonia, D. Uric acid
A: Aspaate and ammonia
Answer: A: Aspaate and ammonia 
Explanation: The 2 nitrogen atoms of urea are derived from two sources, one from ammonia and other from alpha amino group of aspaic acid. Ref: Textbook of Biochemistry By DM Vasudevan, 3rd Edition, Pages 163-5