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
Chlorhexidine on tooth causes 
Select and explain. 
A. No stain, B. Brownish yellow stains, C. Greenish yellow stain, D. Blue back stain
B: Brownish yellow stains
Answer: B: Brownish yellow stains 
Explanation: None