This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Choriocarcinoma, Subject name: Gynaecology & Obstetrics
[{'content': 'Turner syndrome is \nSelect and explain. \nA. 45 XO, B. 47 XXY, C. Trisomy 13, D. Trisomy 18', 'role': 'user'}, {'content': "Answer: A \nExplanation: Ans. (a) 45 XORef: Shaws 15th ed. H10-111; Harrison 19/e 635; William's Gynecology Ch 16", 'role': 'assistant'}]