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: Medicine
[{'content': "Ewa's sign is seen in: \nSelect and explain. \nA. Acute pulmonary embolism, B. Pericardial effusion, C. Pneumomediastinum, D. Chronic constrictive pericarditis", 'role': 'user'}, {'content': "Answer: B \nExplanation: In pericardial effusion the base of the left lung may be compressed by pericardial fluid, producing a patch of dullness and increased fremitus (and egophony) beneath the angle of the left scapula. This is Ewa's sign. Ref: Harrisons principles of internal medicine, 18th edition, Page: 1971.", 'role': 'assistant'}]