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': 'Mastoid reservoir phenomenon is positive in - \nSelect and explain. \nA. CSOM, B. Petrositis, C. Coalescent otitis media, D. Coalescent mastoiditis', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Mastoid reserve phenomenon is filling up of meatus with pus immediately after cleaning. It is seen in mastoiditis.\nRef. SK De, p 107, 98', 'role': 'assistant'}]