This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: General obstetrics, Subject name: Gynaecology & Obstetrics
[{'content': 'The major contribution of the amniotic fluid after 20 weeks of gestation is : \nSelect and explain. \nA. Ultrafiltrate of maternal plasma, B. Fetal urine, C. Fetal lung fluid, D. Fetal skin', 'role': 'user'}, {'content': 'Answer: B \nExplanation: After 20 weeks as the fetal skin becomes keratinized process of diffusion is impaired. In the second half of pregnancy, the fetal kidneys become active and thereafter fetal urine becomes the main source of amniotic fluid. (refer pg no:211 Sheila 2nd edition)', 'role': 'assistant'}]