Right answer is (b) 25 cm
To explain: The user positions themself over the small drop hole during use. The size of the feces drop hole in the floor or slab should not be larger than 25 centimeters (9.8 inches) to prevent children falling in. Light should be prevented from entering the pit to reduce access by flies. This requires the use of a lid to cover the hole in the floor when not in use. However, in practice, such a lid is not commonly used as it is easy to lose it or for the lid to get very filthy.