Only four singers remain on American Idol, and former Idol champ Carrie Underwood claims song choice was an important factor to her winning the crown. Underwood kept her song choices rather simple; if she liked the song and thought she could have done a good job with it, then it was going on the show.  Simple enough, correct? Well of course, like all past Idol winners, a good voice is also a must. (CLICK ON THE MEDIA BAR BELOW TO HEAR CARRIE UNDERWOOD)