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: Unknown
[{'content': 'The key enzyme in urea synthesis is - \nSelect and explain. \nA. Urease, B. Carbamoyl phosphate synthase-I, C. Arginase, D. Ornithine', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans-B', 'role': 'assistant'}]