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: ENT
[{'content': 'The "O" sign in a pure Tone Audiogram indicates - \nSelect and explain. \nA. Air conduction of right ear, B. Air conduction of left ear, C. Bone conduction of right ear, D. Bone conduction of left ear', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]