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': 'True about Eustachian tube - \nSelect and explain. \nA. Length is 36 mm in adults and 1.6 mm to 3 mm in children, B. Higher elastin content in adults, C. Ventilatory function of ear better developed in infants, D. More horizontal in adults', 'role': 'user'}, {'content': 'Answer: B \nExplanation: “Eustachian tube serves to ventilate the middle ear and exchange nasopharyngeal air in the middle ear. In children, ET is relatively\xa0narrow. It is prone to obstructionQ when mucosa swell in response to infection or allergic challenge and it results in middle\xa0ear effusion”', 'role': 'assistant'}]