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: Surgery
Most impoant pre-requisite in sanitary latrine is : 
Select and explain. 
A. Squatting plate or slab, B. Water seal, C. Smooth slope of pan, D. Adequate drainage
B: Water seal
Answer: B: Water seal 
Explanation: Water seal Water seal: The most impoant pa in a sanitary latrine is the water seal. The water seal is the distance between the level of water in the trap & the lowest point in the concave upper surface of the trap It has two impoant functions It prevents access by flies It prevents escapes of odors & foul gases The depth of water seal in the RCA latrine is 2 cm