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': 'Essential radiological feature of acute mastoiditis is - \nSelect and explain. \nA. Temporal bone pneumatisation, B. Clouding of air cells of mastoid, C. Rarefaction of petrous, D. Thickening of temporal bone', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]