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': 'HCG is a tumor marker for : \nSelect and explain. \nA. Choriocarcinoma, B. Colon carcinoma, C. Serous cystadenoma, D. Teratoma', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Choriocarcinoma', 'role': 'assistant'}]