user: Question: Which year had a team of Aprilia and a rank of 4th?
Columns: ['Year', 'Class', 'Team', 'Machine', 'Points', 'Rank', 'Wins']
Types: ['real', 'text', 'text', 'text', 'real', 'text', 'real']
Sample row: [1991.0, '125cc', 'ELF Kepla-Meiko Honda', 'RS125', 55.0, '13th', 0.0]
SQL:

assistant: SELECT "Year" FROM "Table" WHERE "Team" = 'Aprilia' AND "Rank" = '4th';