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
The anatomic crown is shorter than the clinical crown of a tooth in which of the following instances: 
Select and explain. 
A. Impaction, B. Gingivitis, C. Occlusal wear, D. Gingival recession
D: Gingival recession
Answer: D: Gingival recession 
Explanation: None