Please answer the following question: Pick one category for the following text. The options are - company, educational institution, artist, athlete, office holder, mean of transportation, building, natural place, village, animal, plant, album, film or written work. Douglas XB-31 -  The Douglas XB-31 (Douglas Model 423) was the design submitted by Douglas after the request by the United States Army Air Forces for a very heavy bomber aircraft the same request that led to the Boeing B-29 Superfortress Lockheed XB-30 and Consolidated B-32 Dominator.
Answer:
Mean Of Transportation