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 NAVO RK-4/220 was a Dutch aircraft originally designed for unofficial crowd observation but which was completed as an airliner. Only one was built; it flew but was never certified.
Question: The document can be classified to which topic?
Options: 1)Building, 2)Album, 3)Athlete, 4)MeanOfTransportation, 5)Plant
4