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': 'Echocardiography can detect pericardial effusion as little as: \nSelect and explain. \nA. 15 ml, B. 100 ml, C. 150 ml, D. 200 ml', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Ans.', 'role': 'assistant'}]