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': 'What is the most frequent causative agent for acute epiglottitis in children under 5 years of age? \nSelect and explain. \nA. Haemophilus influenzae type B, B. Influenza virus type A, C. Para influenza virus type 1, D. Staphylococcus aureus', 'role': 'user'}, {'content': "Answer: A \nExplanation: a. Haemophilus influenzae type B(Ref: Nelson's 20/e p 2032-2033)Etiology of Epiglottitis: H influenzae type B. Pneumococcus, b-hemolytic Streptococcus and Staphylococccus", 'role': 'assistant'}]