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': 'Commonest tumor of ovary occurring in a young woman is : \nSelect and explain. \nA. Immature teratoma, B. Yolk sac tumor, C. Endometroid tumor, D. Dysgerminoma', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Dysgerminoma', 'role': 'assistant'}]