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: Social & Preventive Medicine
[{'content': 'Most dicient larval control method ent transmission of urban malaria: \nSelect and explain. \nA. Covering overhead tanks, B. Cleaning of drains, C. Filling of ditches and cesspools, D. Uprooting of plants', 'role': 'user'}, {'content': 'Answer: B \nExplanation: Ans. b. Cleaning of drains', 'role': 'assistant'}]