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': 'Crown infarction is \nSelect and explain. \nA. Necrosis of pulp following a fracture, B. An incomplete fracture of enamel without loss of tooth structure, C. Fracture of crown en mass, D. Vertical fracture of crown', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]