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': 'Absolute contraindication for Transvaginal sonography \nSelect and explain. \nA. Placenta previa, B. Imperforate hymen, C. Abruptio placenta, D. Abnormal uterine bleeding', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Imperforate hymen and patient refusal are the only absolute contraindications for Transvaginal sonography.', 'role': 'assistant'}]