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 reservoir phenomenon is the latent infection in the mastoid resulting from inadequate treatment of ASOM. (Also called as masked /latent mastoiditis). It is a slow process of destruction of mastoid air cells without acute features.', 'role': 'assistant'}]