Question: The group that were the singing voices of the Be Sharps on The Simpson's episode "Homer's Barbershop Quartet" have performed at Walt Disney World since what year?

<P0-S0> The Dapper Dans are a barbershop quartet that performs at Disneyland in Anaheim, California (since 1959), at the Magic Kingdom at the Walt Disney World Resort (since 1971), and at Hong Kong Disneyland in Lantau Island, Hong Kong (from 2005 to 2008). <P0-S1>  A quartet (from the UK) also performed at Disneyland Paris from the opening in 1992 until 1995 and were known as the Mainstreet Quartet. <SEP> <P1-S0> "Homer's Barbershop Quartet" is the first episode of "The Simpsons"' fifth season. <P1-S1>  It originally aired on the Fox network in the United States on September 30, 1993. <P1-S2>  The episode was written by Jeff Martin and directed by Mark Kirkland. <P1-S3>  It features the Be Sharps, a barbershop quartet founded by Homer Simpson. <P1-S4>  The band's story roughly parallels that of The Beatles. <P1-S5>  George Harrison and David Crosby guest star as themselves, and The Dapper Dans provide the singing voices of the Be Sharps. <SEP> <P2-S0> SALT is a Swedish barbershop quartet that won the Sweet Adelines International Quartet Championship for 2007 in Las Vegas, Nevada in October 2006. <P2-S1>  Sweet Adelines, "one of the world's largest singing organizations for women", has members over five continents who belong to more than 1200 quartets. <P2-S2>  The quartet placed third at the international contest in 2003 (Phoenix) and 2004 (Indianapolis), and earned a second-place finish in 2005's contest in Detroit. <P2-S3>  SALT's November 2008 feature performance in Anaheim, California, was noted by the Vasa Order of America. <P2-S4>  At the time of winning the Sweet Adelines competition, SALT included tenor Anna Öhman, also a music teacher; lead Annika Andersson, a manager at a social security agency; baritone Anna-Stina Gerdin, an elementary school teacher; and bass Susanna Berndts, a speech therapist. <P2-S5>  Karin Sjöblom later replaced Gerdin as baritone. <P2-S6>  The quartet announced its retirement on Facebook in June 2012 "after singing together for 13 years". <SEP> <P3-S0> The Walt Disney World Dolphin is a resort hotel designed by architect Michael Graves located between Epcot and Disney's Hollywood Studios in the Walt Disney World Resort in Bay Lake, Florida, next to Disney's BoardWalk Resort area. <P3-S1>  It opened on June 1, 1990 and is joined to its sister hotel, the Walt Disney World Swan (also designed by Graves) by a palm-tree lined covered walkway crossing a lagoon. <P3-S2>  The Walt Disney World Swan and Dolphin is a joint venture between the Walt Disney Company, Tishman Hotel Corporation, MetLife and Starwood Hotels and Resorts. <P3-S3>  The land the resort occupies is owned by the Walt Disney Company, while the buildings themselves are leased by Disney to the Tishman Hotel Corporation and MetLife but operated by Starwood Hotels & Resorts Worldwide under the Sheraton Hotels brand. <P3-S4>  The Walt Disney World Swan and Dolphin are a part of the Walt Disney Collection of resorts; because of this they are Disney branded and guests of the resort have access to special Disney benefits available to Disney Resort Hotel guests only.