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
Histology of unicameral bone cyst -a) Blood filled cavitiesb) Endothelial liningc) Giant cellsd) Bone formation 
Select and explain. 
A. cd, B. bc, C. bd, D. ac
A: cd
Answer: A: cd 
Explanation: Simple bone cyst contains clear fluid and consists of flimsy fibrous lining, often containing giant cells.
There is osteoclastic resorption of adjacent bone, (i.e., endosteal osteoclastic resorption) with periosteal new bone formation.