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': 'All of the following are the known causes of osteoporosis except: \nSelect and explain. \nA. Fluorosis, B. Hypogonadism, C. Hyperthyroidism, D. Hyperparathyroidism', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Clinical Features of fluorosis include yellow staining and pitting of permanent teeth, osteosclerosis, soft tissue calciﬁcation, deformities (e.g. kyphosis) and joint ankylosis. Changes in the bones of the thoracic cage may lead to rigidity that causes dyspnoea on exertion.\nDavidson Ed 23 Pg 149', 'role': 'assistant'}]