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 essential investigation to be included In follow-up of hydatidiform mole is : \nSelect and explain. \nA. Ultrasound abdomen, B. Chest X ray, C. Serum levels of HCG, D. Serum levels of TSH', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Serum levels of HCG', 'role': 'assistant'}]