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
[{'content': 'Which substance enters the urea cycle and gets regenerated \nSelect and explain. \nA. Ornithine, B. Aspartate, C. Citrulline, D. Fumarate', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Hence, Urea cycle is also called Ornithine cycle.\nNote: Fumarate does not enter the cycle, it is a by product of the cycle.', 'role': 'assistant'}]