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': 'Marker for ovarian cancer is \nSelect and explain. \nA. CA 125, B. Ca 19 - 19, C. Ca 15 - 5, D. Hypercalcemia', 'role': 'user'}, {'content': 'Answer: A \nExplanation: CA 125', 'role': 'assistant'}]