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: Pathology
[{'content': 'Rootless teeth refer to \nSelect and explain. \nA. Dentin dysplasia, B. Amelogenesis imperfecta, C. Dentinogenesis imperfecta, D. Regional odontodysplasia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]