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: ENT
[{'content': 'The most common cause of cerebrospinal otorrhoea is- \nSelect and explain. \nA. Rupture of tympanic membrance, B. Fracture of petrous ridge, C. Fracture of mastoid air cells, D. Fracture of parietal bone', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]