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': 'Which cephalometric point represents the centre of ramus of mandible? \nSelect and explain. \nA. Xi-point, B. Pm-point, C. Ptm-point, D. N-point', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Xi point:\nA point located at the geometric centre of the ramus. The location of the Xi point can be found geometrically by drawing a line through the porion–orbitale (FH) and perpendicularly through the PT vertical (PTV).', 'role': 'assistant'}]