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': 'CA - 125 is a tumor marker for: \nSelect and explain. \nA. Carcinoma ovary, B. Carcinoma endometrium, C. Carcinoma vagina, D. Carcinoma cervix', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]