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': 'Which of the following is most accurate biometric predictor of gestational age \nSelect and explain. \nA. Head Circumference, B. Crown - rump length, C. Abdominal circumference, D. Gestational sac mean diameter', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Crown - Rump Length is most accurate biometric predictor of gestational age.', 'role': 'assistant'}]