where" isused in an adjectival clause to modify a place (city, country, room, house, etc.). lf where is used, a preposition is NOT included in the adjectival clause. lf where is not used, the preposition must be included. B) He lives in that building. Example: A) The building is very old. The building where he lives is very old. The building in which he lives is very old. The building which he lives in is very old. The building that he lives in is very old. The building he lives in is very old.