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. BT Tower (Birmingham) - The BT Tower (formerly known as the Post Office Tower and before that the GPO Tower) is a landmark in Birmingham England and is also the tallest structure in the city. Its Post Office code was YBMR.
A:
Building