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': 'Ultrasound can detect CVS /cardiac activity at : \nSelect and explain. \nA. 5-6 weeks, B. 6-7 weeks, C. 7-8 weeks, D. 8-10 weeks', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 5-6 weeks', 'role': 'assistant'}]