Use of English PRO

The theory (0) THAT the earth has been visited, perhaps even colonized (1) ............ visitors from outer space has long been a part of popular mythology. The popularity of the theory (2) ............ helped considerably by Stanley Kubrick's cult movie, 2001: A Space Odyssey, which came (3) ............ in 1968 and was instantly a great success. But the idea of visitors (4) ............ space had been very much in the air over the previous twenty years, ever (5) ............ 1947 when a businessman called Kenneth Arnold, who was flying his private plane in Washington state , reported seeing nine shining discs. He said they were moving at an estimated speed of 1,000 miles an hour. This was widely reported in the press and aroused great interest. Soon sightings of unidentified flying objects, or UFOs for short, were being reported all over the world. There were far (6) ............ many of these reports for them to be dismissed (7) ............ pure fantasy. In 1958, in a book entitled Secret Places of the Lion, George Hunt Williamson advanced the theory that visitors from space had arrived ON earth 18 million years (8) ............ and had since been devoting themselves to helping mankind evolve.