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': 'Thumb sign in lateral X- ray of neck seen in - \nSelect and explain. \nA. Epiglottitis, B. Internal haemorrhage, C. Saccular cyst, D. Ca epiglottis', 'role': 'user'}, {'content': 'Answer: A \nExplanation: In epiglottis: A plain lateral soft tissue radiograph of neck shows the following specific features:\nThickening of the epiglottis—the thumb sign\nAbsence of a deep well-defined vallecula—the vallecula sign.\nALSO KNOW \nSteeple sign i.e. narrowing of subglottic region is seen in chest X-ray of patients of laryngotracheobronchitis (i.e. croup).', 'role': 'assistant'}]