Task: Explanation
Input (English): Kellie Pickler is the self-titled second studio album by American country artist Kellie Pickler. The lead-off single, "Don't You Know You're Beautiful", was debuted at the 43rd Academy Of Country Music awards and peaked at 21 on Hot Country Songs. The album was released via BNA Records/19 Recordings on September 30, 2008. Since the albums' release, three more singles have charted; "Best Days of Your Life" at number 9 (which was co-wrote with fellow country artist Taylor Swift), "Didn't You Know How Much I Loved You" at number 14 (a re-recording of an album cut from Pickler's debut album "Small Town Girl") and "Makin' Me Fall in Love Again" at number 30. Question: Which much more famous artist co-writes and sings backing vocals on Kellie Pickler's 2008 song "Best Days of Your Life"? Answer: Taylor Swift
Output (English):  Since the albums release, three more singles have charted; Best Days of Your Life at number 9 which was cowrote with fellow country artist Taylor Swift, Didnt You Know How Much I Loved You at number 14 a rerecording of an album cut from Picklers debut album Small Town Girl and Makin Me Fall in Love Again at number 30.