Answer the following question: I want to test the ability of students to read a passage and answer questions about it. Could you please come up with a good question for the passage "Washington University has been selected by the Commission on Presidential Debates to host more presidential and vice-presidential debates than any other institution in history. United States presidential election debates were held at the Washington University Athletic Complex in 1992, 2000, 2004, and 2016. A presidential debate was planned to occur in 1996, but owing to scheduling difficulties between the candidates, the debate was canceled. The university hosted the only 2008 vice presidential debate, between Republican Sarah Palin and Democrat Joe Biden, on October 2, 2008, also at the Washington University Athletic Complex."?
Answer:
Which was the only year that a presidential debate was held at the mentioned University in the 20th century?