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': 'The gold standard for the diagnosis of osteoporosis is: \nSelect and explain. \nA. Dual energy x-ray absorptiometry, B. Single energy x-ray absorptiometry, C. Ultrasound, D. Quantitative computed tomography', 'role': 'user'}, {'content': 'Answer: A \nExplanation: None', 'role': 'assistant'}]