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 most definitive clinical sign of pregnancy is : \nSelect and explain. \nA. Ballottement, B. Fetal hea sounds, C. Braxton Hick's contraction, D. Enlarged uterus", 'role': 'user'}, {'content': 'Answer: B \nExplanation: Fetal hea sounds', 'role': 'assistant'}]