user: Question: Who won Women's doubles when Raina Tzvetkova won women's singles before 2000?
Columns: ['Year', "Men's singles", "Women's singles", "Men's doubles", "Women's doubles", 'Mixed doubles']
Types: ['real', 'text', 'text', 'text', 'text', 'text']
Sample row: [1985.0, 'Jeliazko Valkov', 'Diana Koleva', 'Ilko Orechov Nanko Ertchopov', 'Diana Koleva Zlatka Valkanova', 'Jeliazko Valkov Dobrinka Peneva']
SQL:

assistant: SELECT "Women's doubles" FROM "Table" WHERE "Year" < 2000.0 AND "Women's singles" = 'Raina Tzvetkova';