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
Lingua nigra is : 
Select and explain. 
A. Familial dysautonomia., B. Hairy tongue., C. Migratory glossitis., D. Median rhomboid glossitis.
B: Hairy tongue.
Answer: B: Hairy tongue. 
Explanation: None