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': 'Most reliable diagnosis of hydatidiform mole is by: \nSelect and explain. \nA. HCG estimation, B. Amniography, C. Ultrasound, D. Absence of FHS', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ultrasound', 'role': 'assistant'}]