Add a background in a platform game

programming flash
1

I am doing a as3 platform game based in arrays, so inside the array I inserted a variable rh that inserts the bg in the stage but it doesn’t show up in the stage. The code i have is:

else if (lvlArray* == 'ROCKYHILLS') {
                    var newRockyHills:backRocky = new backRocky;
                    newRockyHills.x = _root.stage.width/2;
                    newRockyHills.y = _root.stage.height/2;
                    
                    blockHolder.addChild(newRockyHills);
                }

Any suggestions?