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: Radiology
[{'content': 'Best parameter by USG to assess fetal maturity: \nSelect and explain. \nA. Crown rump length at 16 weeks, B. Head circumference at 36 weeks, C. Biparietel diameter at 12 weeks, D. Femur length at 12 weeks', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans. Biparietel diameter at 12 weeks', 'role': 'assistant'}]