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': 'A good trap should have effective seal of \nSelect and explain. \nA. 2.5 cm, B. 5 cm, C. 7.5 cm, D. 10 cm', 'role': 'user'}, {'content': 'Answer: B \nExplanation: • The trap: Is a bent pipe in sanitary latrine, about 7.5 cms in diameter and connected with the pan\nTrap is a ‘Water seal’: it holds water; prevents access by flies and suppresses the nuisance from smell\nDepth of water seal in RCA sanitary latrine: 2 cms (¾ inch)\nWater seal in sanitary latrine is an example of ‘Sanitation barrier.’', 'role': 'assistant'}]