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': 'Best investigation to diagnose fetal age is : \nSelect and explain. \nA. Serial Ultrasound, B. Amniocentesis, C. Fundal height measurement, D. X-ray', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Serial Ultrasound', 'role': 'assistant'}]