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 hemorrhage, 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 Thickening of the epiglottis--the thumb sign Absence of a deep well-defined vallecula--the vallecula sign Steeple sign i.e. Narrowing of subglottic region is seen in chest X-ray of patients of laryngotracheobronchitis (i.e. croup).', 'role': 'assistant'}]