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': 'The earliest diagnostic test of pregnancy : \nSelect and explain. \nA. Ultrasound, B. Beta HCG, C. Fetal movements, D. Fetal hea sounds', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Beta HCG', 'role': 'assistant'}]