One significant feature of the Premier League in the mid-2000s was the dominance of the so-called "Big Four" clubs: Arsenal, Chelsea, Liverpool and Manchester United. During this decade, and particularly from 2002 to 2009, they dominated the top four spots, which came with UEFA Champions League qualification, taking all top four places in 5 out of 6 seasons from 2003–04 to 2008–09 inclusive, with Arsenal going as far as winning the league without losing a single game in 2003–04, the only time it has ever happened in the Premier League. In May 2008 Kevin Keegan stated that "Big Four" dominance threatened the division, "This league is in danger of becoming one of the most boring but great leagues in the world." Premier League chief executive Richard Scudamore said in defence: "There are a lot of different tussles that go on in the Premier League depending on whether you're at the top, in the middle or at the bottom that make it interesting."

Answer this question, if possible (if impossible, reply "unanswerable"): Which of the "Big Four" teams did not lose a single game in the 2003-04 season?
Arsenal