This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: All India exam, Subject name: Radiology
[{'content': 'Gamma camera is used for \nSelect and explain. \nA. Organ imaging, B. Measuring radioactivity, C. Monitoring surface contamination, D. RIA', 'role': 'user'}, {'content': 'Answer: B \nExplanation: (Ref: Grainger&;s diagnostic radiology, 6th ed; page 120)', 'role': 'assistant'}]