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': 'A lady has ovarian mass, x-ray pelvis shows a radio-opaque shadow. The probable diagnosis is: \nSelect and explain. \nA. Mucinous cyst adenoma, B. Serous cyst adenoma, C. Dysgerminoma, D. Dermoid cyst', 'role': 'user'}, {'content': 'Answer: D \nExplanation: None', 'role': 'assistant'}]