Task: Explanation
Input (English): "Best Days of Your Life" is a song written and performed by American country artist Kellie Pickler, and co-written by Taylor Swift. It was released on December 1, 2008 as the second single from her self-titled second album. Swift also provides background vocals on the song. The song is about a narrator explaining how her former boyfriend cheated on her and moved on to a new girlfriend to start a family with, wishing them well on their new life but says that the new girl won't top what they previously once had before. 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):  Swift also provides background vocals on the song.