user: Question: Which Opponents have a Year of 1999–2000, and a Team of Leeds United?
Columns: ['Year', 'Team', 'Progress', 'Score', 'Opponents']
Types: ['text', 'text', 'text', 'text', 'text']
Sample row: ['1955–58', 'Birmingham City', 'Semi-finals', '1–2 (Playoff)', 'Barcelona']
SQL:

assistant: SELECT "Opponents" FROM "Table" WHERE "Year" = '1999–2000' AND "Team" = 'Leeds United';