Put questions (all types) to the sentence foundations serve to keep the walls and floors from contact with the soil

Foundations serve to keep the walls and floors from contact with the soil, don't they?
Do foundations serve to keep the walls and floors from contact with the soil?
Do foundations serve to keep the walls or floors from contact with the soil?
What serves to keep the walls and floors from contact with the soil?
What do foundations serve to keep from contact with the soil?