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
Down's syndrome patients shows: 
Select and explain. 
A. Early exfoliation of deciduous teeth, B. Microdontia of teeth over retained teeth, C. Periodontitis, D. All of the above
D: All of the above
Answer: D: All of the above 
Explanation: None