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
Bone density is decreased in which of the following - 
Select and explain. 
A. Osteoporosis, B. AVN of bone, C. 0steopetrosis, D. Fracture and collapse of cancellous bone
A: Osteoporosis
Answer: A: Osteoporosis 
Explanation: Osteoporosis is characterized by an abnormally low bone mass (reduced bone density) and defects in bone structure.