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': 'Conventional unit of Exposure is: \nSelect and explain. \nA. C/Kg, B. Air Kerma, C. Roentgen, D. Rad', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Units (Dosimetry) (Very important):', 'role': 'assistant'}]