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
Hydroxyapatite coating of dental implants was introduced by 
Select and explain. 
A. DeGroot, B. Hahn and Polich, C. Kay, D. Clemow
A: DeGroot
Answer: A: DeGroot 
Explanation: None