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: Medicine
[{'content': 'The toxicity of etambutol includes one of the following: \nSelect and explain. \nA. Peripheral neuritis, B. Green colour blindness, C. Red urine, D. Yellow colour blindness', 'role': 'user'}, {'content': 'Answer: B \nExplanation: The optic neuritis is the most serious side effect of ethambutol manifesting as reduced visual acuity, central scotoma, and loss of ability to see green colour. Ref: Harrisons Principles of Medicine, 18th edition, page : 1375', 'role': 'assistant'}]