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': 'Attenuation value (Hounsfield unit) of -1000 represents which of the following? \nSelect and explain. \nA. Air, B. Muscle, C. Bone, D. Blood', 'role': 'user'}, {'content': 'Answer: A \nExplanation: The HU for common substance: SUBSTANCE HU Air -1000 Fat -120 (Range -50 to -120) Water 0 Blood +30 to +45 Muscle +40 Contrast +130 Bone +400 Reference: Essential Radiology By S.Bhadury, 2nd Edition, Page 23', 'role': 'assistant'}]