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WikiPedia: Vụ_UFO_Levelland http://www.myfoxdfw.com/story/17512052/the-tex-fil... http://files.ncas.org/ufosymposium/mcdonald.html https://books.google.com/books?id=IYNTAAAAMAAJ https://books.google.com/books?id=d9BaAAAAYAAJ https://books.google.com/books?id=q2tVPgAACAAJ https://books.google.com/books?id=zjI4X7ZOvOIC https://news.google.com/newspapers?nid=1946&dat=19... https://web.archive.org/web/20130427001653/http://...