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: Physiology
[{'content': 'The intrapleural pressure is negative both during inspiration and expiration because: \nSelect and explain. \nA. Intrapulmonary pressure is always negative, B. Thoracic cage and lungs are elastic structure, C. Transpulmonary pressure determines the negativity, D. All', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Thoracic cage and lungs are elastic structures', 'role': 'assistant'}]