Question: When did the washington nationals become a baseball team?

Disambiguated questions and answers:
context: On September 29, 2004, MLB announced the Expos would move to Washington, D.C., in 2005. On November 15, a lawsuit by the former team owners against MLB and former majority owner Jeffrey Loria was struck down by arbitrators, bringing to an end all legal actions that would impede a move. The owners of the other MLB teams approved the move to Washington, D.C., in a 28–1 vote on December 3 (Baltimore Orioles owner Peter Angelos cast the sole dissenting vote).
question: When was the official announcement that the Washington Nationals would be a baseball team?
short_answers: September 29, 2004
wikipage: Washington Nationals

context: The Washington Nationals are an American professional baseball team based in Washington, D.C. The Nationals compete in Major League Baseball (MLB) as a member club of the National League (NL) East division. From 2005 to 2007, the team played in RFK Stadium while their permanent stadium was being built. In 2008, they moved in to Nationals Park, located on South Capitol Street in the Southeast quadrant of D.C., near the Anacostia River.
question: For what MLB baseball season did the Washington Nationals become a baseball team?
short_answers: 2005
wikipage: Washington Nationals

Long answers:
knowledge: content: The Washington Nationals are an American professional baseball team based in Washington, D.C. The Nationals compete in Major League Baseball (MLB) as a member club of the National League (NL) East division. From 2005 to 2007, the team played in RFK Stadium while a new stadium was being built. In 2008, they moved in to Nationals Park, located on South Capitol Street in the Southeast quadrant of D.C., near the Anacostia River.
wikipage: Washington Nationals

content: On September 29, 2004, MLB announced the Expos would move to Washington, D.C., in 2005.[31][32] On November 15, a lawsuit by the former team owners against MLB and former majority owner Jeffrey Loria was struck down by arbitrators, bringing to an end all legal actions that would impede a move. The owners of the other MLB teams approved the move to Washington, D.C., in a 28–1 vote on December 3 (Baltimore Orioles owner Peter Angelos cast the sole dissenting vote).
wikipage: Washington Nationals

content: The current franchise was founded in 1969 as the Montreal Expos as part of a four-team expansion. After a failed contraction plan, the Expos were purchased by MLB, which sought to relocate the team to a new city.[6] Washington, D.C. was chosen in 2004, and the Nationals were established in 2005 as the first MLB franchise relocation since the third Washington Senators moved to Texas in 1971.
wikipage: Washington Nationals
long_answer: The Washington Nationals are an American professional baseball team based in Washington, D.C. that were originally founded in 1969 as the Montreal Expos. After a failed contraction plan, the Expos were purchased by MLB, which sought to relocate the team to a new city. On September 29, 2004, MLB announced the Expos would move to Washington, D.C. The Nationals were established in 2005 as the first MLB franchise relocation since the third Washington Senators moved to Texas in 1971.