This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Infections and Inflammatory Conditions, Subject name: ENT
[{'content': 'A child presents with fever, stridor and barking cough. His X-ray is given below: Following is true about the patient: \nSelect and explain. \nA. Symptoms are predominantly caused by involvement of subglottis, B. Antibiotics should be started immediately, C. X-ray is showing thumb sign, D. Caused by H. influenzae b', 'role': 'user'}, {'content': 'Answer: A \nExplanation: (a) Symptoms are predominantly caused by involvement of subglottis(Ref. Cummings, 6th ed., 3049; Scott Brown, 8th ed., Vol 1; 326)', 'role': 'assistant'}]