共用题干第一篇Unidentified Flying Object

共用题干

第一篇

Unidentified Flying Object

Unidentified flying Object(UFO)is any object or light,reportedly sighted in the sky,that cannot be immediately explained by the observer. Sightings of unusual aerial phenomena date back to ancient times,but UFOs(sometimes called flying saucers)became widely discussed only after the first widely publicized U.S.sighting in 1947.Many thousands of such observations have since been reported worldwide.
At least 90 percent of UFO sightings can be identified as conventional objects,although time consuming investigations are often necessary for such identification.The objects most often be mistaken for UFOs are bright planets and stars,aircraft,birds,balloons,kites,aerial flares,peculiar clouds, meteors（流星）,and satellites. The remaining sightings most likely can be attributed to other mistaken sightings or to inaccurate reporting, tricks, or delusions（妄想）,although to disprove all claims made about UFOs is impossible.
From 1947 to 1969 the US air force investigated UFOs as a possible threat to national security. A total of 12,618 reports was received,of which 701 reports,or 5.6 percent,were listed as unexplained.The air force concluded that"no UFO reported,investigated,and evaluated by the Air Force has ever given any indication of threat to our national security."Since 1969 no agency of the US government has had any active program of UFO investigation.
Some persons, however, believe that UFOs are extraterrestrial（地球外的）spacecraft, even though no scientifically valid evidence supports that belief. The possibility of extraterrestrial civilizations is not the stumbling block（障碍物）;most scientists grant that intelligent life may well exist elsewhere in the universe.A fully convincing UFO photograph of a craft like object has yet to be taken, however, and the scientific method requires that highly speculative（推测性的）explanations should not be adopted unless all of the more ordinary explanations can be ruled out.
UFO enthusiasts persist,however,and some persons even claim to have been captured and taken aboard UFOs.No one has produced scientifically acceptable proof of these claims.Behavioral scientist Car Sagan of Cornel University has proposed that"certain psychological needs are met by belief in superior beings from other worlds."

How does Carl Sagan feel about the UFO enthusiasts? A:Talking about encounters with visitors from outer space may satisfy them psychologically. B:They refuse to accept the possibility that UFOs are some conventional objects. C:They are reluctant to look for scientifically acceptable evidence for their claims. D:Their curiosity drives them to adopt the highly speculative explanations about UFOs.