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': 'Fetal hea can be detected earliest with trans-vaginal sonography at (from the last menstrual period) : \nSelect and explain. \nA. 35 days, B. 38 days, C. 53 days, D. 46 days', 'role': 'user'}, {'content': 'Answer: D \nExplanation: 46 days', 'role': 'assistant'}]