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
Osteitis fibrosa cystica refers to: 
Select and explain. 
A. Paget's disease., B. Fibrous dysplasia., C. Hyperparathyroidism., D. Osteogenesis imperfecta.
C: Hyperparathyroidism.
Answer: C: Hyperparathyroidism. 
Explanation: None