In this task, you are given a text which is the body of a document. You are given a question and options. Pick the correct number. Don't generate anything else apart from the numbers provided in options.

Context: The Udet U 12 Flamingo was an aerobatic sports plane and trainer aircraft developed in Germany in the mid-1920s. It was a conventional single-bay biplane of wooden construction with the wings braced by large I-struts. The pilot and instructor or passenger sat in tandem open cockpits. The U 12 proved extremely popular and sold well due in no small part to Ernst Udet's spectacular aerobatics routines while flying the aircraft.
Question: The document can be classified to which topic?
Options: 1)Artist, 2)Building, 3)MeanOfTransportation, 4)Company, 5)Plant
3