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': 'Which of the following is true about pleural effusiona) Horizontal fluid levelb) Low lung volumec) Muffled heart sounds  d) Decreased chest movementse) Succussion splash \nSelect and explain. \nA. bcd, B. acd, C. ac, D. bd', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]