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: Dental
Osteoblast covering the periodontal surface of the alveolar bone constitute a 
Select and explain. 
A. Modified periosteum, B. modified endosteum, C. periosteum, D. endosteum
B: modified endosteum
Answer: B: modified endosteum 
Explanation: None