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: Pharmacology
A patient of multidrug resistant tuberculosis is on antitubercular drugs. After a few months he develops an inability to distinguish between red and green color. Most likely drug causing these symptoms is : 
Select and explain. 
A. Rifampicin, B. Ethambutol, C. Cycloserine, D. Ethionamide
B: Ethambutol
Answer: B: Ethambutol 
Explanation: None