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1. UFOs are strange flying objects that some people report they have seen in the sky and believed to be spacecraft from another planet. Many scientists do not believe so. They say that if people see a UFO, it might be an  , a weather balloon or a meteor. However, there is still evidence for people to believe in the   of UFOs.
In 1947, Kenneth Arnold, an experienced pilot in the USA, reported that he saw nine large round   traveling at about 2,800 meters an hour to the left and north of Mount Rainier.
In 1952, there were more than 1,500 UFO   around the world.