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': 'VRF vertical root fracture primarily occurs in which direction? \nSelect and explain. \nA. Mesiodistal, B. Faciolingual, C. Coronal and extending apically, D. No primary direction', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]