Given the task definition and input, reply with output. This task is about reading the given passage and construct a question about the information present in the passage. Construct a question in such a way that (i) it is unambiguous, (ii) it is answerable from the passage, (iii) its answer is unique (iv) its answer is a continuous text span from the paragraph. Avoid creating questions that (i) can be answered correctly without actually understanding the paragraph and (ii) uses same words or phrases given in 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.
What years were presidential debates held at Washington University?