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': 'Lecithin-Sphingomyelin ratio is used for: \nSelect and explain. \nA. Lung maturity, B. Age of infant, C. Kidney maturity, D. Brain maturity', 'role': 'user'}, {'content': "Answer: A \nExplanation: a. Lung maturity(Ref: Nelson's 20/e p 2088-2093, Ghai 8/e p 379-381)By 35 wk of gestation, the lecithin: sphingomyelin (L:S) ratio averages about 2:1, indicative of lung maturity.", 'role': 'assistant'}]