This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Ocular Manifestations, Subject name: Ophthalmology
[{'content': 'River blindness is caused by : \nSelect and explain. \nA. Drinking river water without boiling., B. Oncocerca volvulus, C. Toxoplasma canis, D. Glaucoma', 'role': 'user'}, {'content': "Answer: B \nExplanation: Ans. is 'b' i.e. Onchocerca volvulus Onchocerca volvulus is transmitted by Simulium damnosum, a black fly* that breeds in areas of rapidly flowing streams thus the term 'river blindness9T/t by Ivermectin*", 'role': 'assistant'}]