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': "Dummer's classification is associated with \nSelect and explain. \nA. Apical constriction, B. Apical foramen, C. Root canal Isthmus, D. No of canals", 'role': 'user'}, {'content': 'Answer: A \nExplanation: Dummer’s classification of topography of apical constriction', 'role': 'assistant'}]