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: Gynaecology & Obstetrics
[{'content': "Stain used for maturity assessment of amniotic fluid cells : \nSelect and explain. \nA. Leishman's stain, B. Sudan red, C. Nile blue sulfate, D. Congo red", 'role': 'user'}, {'content': 'Answer: C \nExplanation: Nile blue sulfate', 'role': 'assistant'}]