This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory System, Subject name: Pediatrics
[{'content': 'Lateral X-ray of the upper airway in a 2-year-old boy reveals a "thumb sign". The most likely diagnosis is: \nSelect and explain. \nA. Laryngeal polyps, B. Epiglottitis, C. Subglottic hemangioma, D. Laryngeal edema', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B. EpiglottitisEpiglottitis is characterized by inflammatory edema of the epiglottis along with upper airway obstruction. It is usually a cause of severe respiratory distress in young children and is associated with sudden onset high fever, drooling of saliva and the child in a typical "tripod position". Cause is usually S. pneumonia, or less frequently, H. influenza.', 'role': 'assistant'}]