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: Pathology
Erlenmeyer flask deformity of bones is seen in? 
Select and explain. 
A. Achondroplasia, B. Osteopetrosis, C. Osteogenesis Imperfecta, D. Pagets disease
B: Osteopetrosis
Answer: B: Osteopetrosis 
Explanation: Due to deficient osteoclast activity bones lack medullary canal and the ends become bulbous giving rise to Erlenmeyer flask deformity.