This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ultrasonography, CT, and MRI, Subject name: Radiology
[{'content': 'Hounsfield unit is zero for which of the following_____: \nSelect and explain. \nA. Air, B. Water, C. Fat, D. Dense bone', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. B. Water* Water is arbitrarily assigned a value of 0HUHU of different tissues of body:* Cortical Bone:+1000HU (Bright white)* Solid soft tissue: from +40 to +80HU (sometimes upto +300)* Acute hemorrhage:+45 to+65 HU* Water: 0HU (Grey)* Fat:-100HU* Lungs:-950 to-700HU* Air:-1000HU (Jet black)* In CT, bone and hemorrhage are white, air and fat is black.', 'role': 'assistant'}]