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
Following scaling a patient notices hard black deposits. This may be due to: 
Select and explain. 
A. Shrinkage of gingiva, B. Patient is heavy tea drinker, C. Poor home care, D. Blood clot formation on tooth surface
A: Shrinkage of gingiva
Answer: A: Shrinkage of gingiva 
Explanation: None