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': 'Narrowest part of zipping canal is known as \nSelect and explain. \nA. Minor Diameter, B. Major Diameter, C. Isthmus, D. Elbow', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]