Arsenal F.C.:

Highbury could hold more than 60,000 spectators at its peak, and had a capacity of 57,000 until the early 1990s. The Taylor Report and Premier League regulations obliged Arsenal to convert Highbury to an all-seater stadium in time for the 1993–94 season, thus reducing the capacity to 38,419 seated spectators. This capacity had to be reduced further during Champions League matches to accommodate additional advertising boards, so much so that for two seasons, from 1998 to 2000, Arsenal played Champions League home matches at Wembley, which could house more than 70,000 spectators.

Please answer a question about this article. If the question is unanswerable, say "unanswerable". During what time did Arsenal play at Wembley?
1998 to 2000