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: Surgery
[{'content': 'Investigation of choice for submandibular sialolithiasis is \nSelect and explain. \nA. Sialography, B. CT scan, C. USG, D. X-ray', 'role': 'user'}, {'content': 'Answer: D \nExplanation: X ray is IOC for submandibular sialolithiasis as most of the stones are radio-opaque.', 'role': 'assistant'}]