CREATE TABLE table_21696 ("Winner" TEXT, "Country" TEXT, "Winter Olympics" TEXT, "FIS Nordic World Ski Championships" TEXT, "Holmenkollen" TEXT)

What years did Birger Ruud win the FIS Nordic World Ski Championships?
SELECT "FIS Nordic World Ski Championships" FROM table_21696 WHERE "Winner" = 'Birger Ruud'
SELECT "FIS Nordic World Ski Championships" FROM "table_21696" WHERE "Winner" = 'Birger Ruud'