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
Study of oral tissue by decalcification method is useful for: 
Select and explain. 
A. Enamel., B. Pulp., C. Cementum., D. PDL.
C: Cementum.
Answer: C: Cementum. 
Explanation: Study of oral tissue by decalcification method is not useful for enamel, pulp, pdl.