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 common pure germ cell tumour of the ovary: \nSelect and explain. \nA. Choriocarcinoma, B. DysgerminOma, C. Embryonal cell tumor, D. Malignant Teratoma', 'role': 'user'}, {'content': 'Answer: B \nExplanation: None', 'role': 'assistant'}]