CREATE TABLE table_79143 ("Date" TEXT, "Bowl Game" TEXT, "Big Ten Team" TEXT, "Opp. Team" TEXT, "Score" TEXT)

Who was the opposing team in the game with a score of 21-17?
SELECT "Opp. Team" FROM table_79143 WHERE "Score" = '21-17'
SELECT "Opp. Team" FROM "table_79143" WHERE "Score" = '21-17'