For thousands of years, people have seen things they 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 no more than a weather balloon or an airplane. But the Center for UFO Studies goes on to receive hundreds of reports each 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 they looked like "pie plates skipping over water." The reporter used the words "flying saucer " in his story and today that is the popular name for UFOs. The Center for UFO Studies lists three kinds of contacts 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. The Center for UFO Studies   _  .
usually sees no more than a weather balloon or an airplane every year is a branch of the United States Air Force receive hundreds of reports every year used "pie plates skipping over water" to describe the UFO seen by the people first
Question: For thousands of years, people have seen things they 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 no more than a weather balloon or an airplane. But the Center for UFO Studies goes on to receive hundreds of reports each 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 they looked like "pie plates skipping over water." The reporter used the words "flying saucer " in his story and today that is the popular name for UFOs. The Center for UFO Studies lists three kinds of contacts 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. The Center for UFO Studies   _  .
A. usually sees no more than a weather balloon or an airplane every year
B. is a branch of the United States Air Force
C. receive hundreds of reports every year
D. used "pie plates skipping over water" to describe the UFO seen by the people first
Answer: