Correct option is (d) shelter
The best I can explain: A shelter, shed, small building or “super-structure” houses the squatting pan or toilet seat and provides privacy and protection from the weather for the user. Ideally, the shelter or small building should have hand washing facilities available inside or on the outside (e.g. supplied with water from a rainwater harvesting tank on the roof of the shelter) although this is unfortunately rarely the case in practice. In the shelter, anal cleansing materials (e.g. toilet paper) and a solid waste bin should also be available. A more substantial structure may also be built, commonly known as an outhouse.