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': 'Commonest cause of Eustachian tube diseases - \nSelect and explain. \nA. Adenoids, B. Sinusitis, C. Otitis media, D. Pharyngitis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]