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: Medicine
[{'content': 'Investigation of choice for pancreatic islet cell tumour is - \nSelect and explain. \nA. CT scan, B. MRI, C. Nuclear scan, D. USG', 'role': 'user'}, {'content': 'Answer: C \nExplanation: None', 'role': 'assistant'}]