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: Pathology
Disease which increases oral melanin pigmentation: 
Select and explain. 
A. addison's disease, B. Hyperthyroidism, C. Nephritis, D. All of the above
A: addison's disease
Answer: A: addison's disease 
Explanation: None