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 one of the following amino acids is purely ketogenic? \nSelect and explain. \nA. Proline, B. Phenylalanine, C. Isoleucine, D. Leucine', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]