This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Gynaecology & Obstetrics
[{'content': 'Most accurate tool for gestational age assignment is \nSelect and explain. \nA. Menstrual history, B. Clinical assessment, C. First trimester Crown-Rump length, D. Femur length', 'role': 'user'}, {'content': "Answer: C \nExplanation: A first-trimester crown rump length is the most accurate tool for gestational age assignment and is performed as clinically indicated. (Ref: William's Obstetrics; 25th edition)", 'role': 'assistant'}]