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': 'Definitive sign of pregnancy : \nSelect and explain. \nA. Uterine souffle, B. Ballottement, C. Fetal hea sound, D. Amenorrhea', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Fetal hea sound', 'role': 'assistant'}]