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
The key enzyme in urea synthesis is - 
Select and explain. 
A. Urease, B. Carbamoyl phosphate synthase-I, C. Arginase, D. Ornithine
B: Carbamoyl phosphate synthase-I
Answer: B: Carbamoyl phosphate synthase-I 
Explanation: Ans-B