A UFO (Unidentified Flying Object) is any object (1) ………………… in the sky which can be unidentified by the person who (2) …………………it. Sometimes the object is investigated. If people cannot figure (3) ………………… what the object is after an investigation, it is called a UFO. If they figure out what the object is, it can no (4) ………………… be called a UFO because it has been identified. Even though UFOs can be anything, people can (5) ………………… the word UFO when they are talking about aliens’ spacecraft. Flying saucer is another (6) ………………… that is often used to describe an identified flying (7) ………………… Studies estimate that 50-90% of all reported sightings are identified later. Usually 10-20% are never identified. Studies also (8) ………………… that very few UFO sightings are hoaxes (people trying to trick other people). Most UFOs are actually natural or man-made objects that (9) ………………… strange. 80-90% of UFOs are identified as one of these different things: (a) astronomical causes (for example: planets, stars, or meteors); (b) aircraft; and (c) balloons. 10-20% of UFOs are other causes, (10) ………………… as birds, clouds, mirages, searchlights, etc.