Question: William Aiken House and Associated Railroad Structures is a historic district in Charleston South Carolina that contains structures of South Carolina Canal and Rail Road Company and the home of the company's founder William Aiken. These structures are considered nationally significant in relation to the history of the development of the railroad industry in the United States. Given a list of categories: company, educational institution, artist, athlete, office holder, mean of transportation, building, natural place, village, animal, plant, album, film or written work, what category does the paragraph belong to?
Answer:
Building