Carrie Underwood has really popped. The pregnant singer showed off her biggest baby bump yet while performing Thursday at the Grand Ole Opry in Nashville to honor late country singer Little Jimmy Dickens. During the tribute show, which also served as a funeral for Dickens, Underwood took the stage in a tight black dress that hugged her growing belly adorably. Underwood paired her simple dress with a black and white scarf around her neck. The 31-year-old American Idol winner and mother-to-be looking glowing—yet-mournful—as she belted out songs in honor of Dickens. Underwood also took to Twitter to pay her respects to the icon, who passed away on Jan. 2 at the age of 94. "I know why it's...