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': 'The following will be most helpful radiological investigation in a patient suspected of left pleural effusion \nSelect and explain. \nA. Right lateral decubitus, B. Left lateral decubitus, C. Left lateral erect, D. Right lateral erect', 'role': 'user'}, {'content': 'Answer: B \nExplanation: B i.e. Left lateral decubitus', 'role': 'assistant'}]