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': 'Cavities beginning in the proximal surfaces of bicuspids and molars are \nSelect and explain. \nA. Class 1, B. Class 2, C. Class 4, D. Class 6', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]