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: Anatomy
[{'content': 'Earliest of fetal hea can be detected at: \nSelect and explain. \nA. 6-6.5 weeks, B. 6.5-7 weeks, C. 7.1-7.5 weeks, D. 8 weeks', 'role': 'user'}, {'content': "Answer: A \nExplanation: When the question says - Cardiac activity is earliest detected at it means it's about TVS (Transvaginal sonography),which is seen at 6 weeks. Ref: Callen 4e pg 119,120.", 'role': 'assistant'}]