The Great Exhibition held in London in 1851 was probably the first show to be called a world fair.Since then there have been 31 universal exhibitions and many cities26to have a world fair.In 1928 the International Bureau of Expositions was founded in Paris to co-ordinate these events and ensure that there is only one each year.There are various and interlinked objectives27holding a world fair.The stated objectives include encouraging trade，increasing the visibility of a city and country, developing tourism，28economic development and increasing employment，stimulating the re-use of land and29improvements，the celebration of a past event，and the entertainment of the masses，30the often unstated one of obtaining31funds from the higher levels of government.The32motive for holding a world fair is to33the city ,but as well as selling the city ,there is also the selling of ideas.Most expos are linked in some way to the notion of the progress of civilization or modernity.Not34，Expo 92 in Seville，Spain，had the35of discovery.Other themes include education and international understanding.The36city usually prepares a special site for the event37new buildings and structures of hoped-for architectural distinction and image changing ability are erected. Early examples38London’s Crystal Palace and Paris’s Eiffel Tower and a more recent one is Seattle’s Space Needle.These structures will remain a39legacy to the area,as will any general infrastructure put in place.The fair itself usually contains exhibitions of both arts and manufactures，with pavilions40also by foreign nations.World fairs usually last between five and seven months，but sometimes they last for a whole year.

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