This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Skeletal System, Subject name: Radiology
Bone in bone appearance is seen in- 
Select and explain. 
A. Active scurvy, B. AML, C. Osteopetrosis, D. Osteosarcoma
C: Osteopetrosis
Answer: C: Osteopetrosis 
Explanation: Ans. is 'c' i.e., Osteopetrosis * Bone within a bone is a descriptive term applied to bones that appear to have another bone within them.* Bone within a bone appearance is seen in : - Normal neonate, Prostaglandin El therapy, Growth arrest/recovery lines n Heavy metal (e.g., Lead) poisoning, Bisphosphonate therapy, Hypothyroidism & Hypoparathyroidism, Sickle cell anemia n Hypercalcemia & Hypervitaminosis D, Osteopetrosis, Rickets / Osteomalacia (healed phase), Acromegaly, Scurvy (healed phase).