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
A good trap should have effective seal of 
Select and explain. 
A. 2.5 cm, B. 5 cm, C. 7.5 cm, D. 10 cm
B: 5 cm
Answer: B: 5 cm 
Explanation: • The trap: Is a bent pipe in sanitary latrine, about 7.5 cms in diameter and connected with the pan
Trap is a ‘Water seal’: it holds water; prevents access by flies and suppresses the nuisance from smell
Depth of water seal in RCA sanitary latrine: 2 cms (¾ inch)
Water seal in sanitary latrine is an example of ‘Sanitation barrier.’