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 serum tumor maker for trophoblastic tumor is : \nSelect and explain. \nA. a HCG, B. Calcitonin, C. b HCG, D. g HCG', 'role': 'user'}, {'content': 'Answer: C \nExplanation: b HCG', 'role': 'assistant'}]