I haven't taken biology since my freshman year of high school, so this is kind of a guess. But I know for sure it isn't a solid. So I would go with a gas.
An exposure to constant or prolonged stimulus will slowly decrease our response.
For example, when we rested our arm or hand on the table then the surface of the table will abruptly feel against our hand.
Sensory adaptation helps us in daily life work by decreasing our response to constant stimulus that's why we give our attention to other environmental aspects. If our response will remain constant to prolonged stimulus then we can't detect new or important environmental aspects.
