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: Orthopaedics
Avascular necrosis is seen in -a) Sickle cell diseaseb) Thalassemiac) Polycythemiad) Hyperparathyroidism 
Select and explain. 
A. a, B. bc, C. ac, D. b
C: ac
Answer: C: ac 
Explanation: Sickle cell anemia and polycythemia can cause AVN.