Birger Ruud ชนะการแข่งขัน FIS Nordic World Ski Championships กี่ปี?ไม่จำเป็นต้องใช้โต๊ะทั้งหมด
What years did Birger Ruud win the FIS Nordic World Ski Championships?It is not neccessary to use all the tables.
 table_21696:  "Winner" [ text]  "Country" [ text]  "Holmenkollen" [ text] 
SELECT "FIS Nordic World Ski Championships" FROM table_21696 WHERE "Winner" = 'Birger Ruud'