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': 'The major contribution of the amniotic fluid after 20 weeks of gestation: \nSelect and explain. \nA. Ultrafiltrate and maternal plasma, B. Fetal urine, C. Fetal lung fluid, D. Fetal skin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Origin of amniotic fluid:', 'role': 'assistant'}]