There is something people didn't understand in the sky.The United States Air Force first used the words "Unidentified Flying Object" to describe them.Today everyone uses the term UFO.When people see a UFO,it is usually a weather balloon or an airplane.But the Center for UFO Studies continues to receive hundreds of reports every year.
In 1947 a businessman and pilot,Kenneth Arnold,was flying near Mount Rainier,Washington when he saw nine shiny,round objects flying through the air.He told a newspaper reporter that they looked like "pie plates skipping over water".The reporter used the words "flying saucer（飞碟）" in his story and today that is a popular name for UFOs.
The Center for UFO Studies shows three kinds of encounters（相遇）with flying saucers."Encounters of the first kind" are reports of unknown objects or lights in the sky.People have "Encounters of the second kind" when a UFO leaves burn marks or other signs on the ground.People report "Close encounters of the third kind" when they see aliens in or near a UFO.
1.What does the UFO stand for?
_____________________________________________________________________________ 2.Does the Center for UFO Studies receive many reports about the UFO every year?
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3.When was the term "flying saucer" used first?
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4.What did Kenneth Arnold do?
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5.How many kinds of encounters with flying saucers does the Center for UFO Studies show?
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