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: Radiology
[{'content': 'Anomaly scan is done at _______ weeks of gestation \nSelect and explain. \nA. 16, B. 18, C. 20, D. 22', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Anamoly scan is done at 18 - 20 weeks best done at 20 weeks.', 'role': 'assistant'}]