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
All of the following are the known causes of osteoporosis except : 
Select and explain. 
A. Fluorosis, B. Hypogonadism, C. Hypehyroidism, D. Hyperparathyroidism
A: Fluorosis
Answer: A: Fluorosis 
Explanation: Answer is A (Fluorosis): Fluorosis is associated with `Osteosclerosis' and not with osteoporosis. Hypogonodism, Hypehyrodism and Hyperparathyrodism are all known causes for osteoporosis.