This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Anatomy
[{'content': 'The longest duration of action of insulin preparation is obtained with \nSelect and explain. \nA. Crystal zinc insulin, B. Insulin zinc suspension (Semilente), C. Protamine zinc insulin, D. Isophane insulin', 'role': 'user'}, {'content': 'Answer: C \nExplanation: (Refer Q 17)', 'role': 'assistant'}]