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: Dental
[{'content': 'Matrix band is difficult to place on -- teeth \nSelect and explain. \nA. MO 25, B. DO 37, C. DO 24, D. MO 24', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]