import flash.display.BitmapData;
var bgImage:BitmapData = BitmapData.loadBitmap("bg" + _root.bgNum );
_root.bg.attachBitmap(bgImage, 0, "auto", true);
var bgImage:BitmapData = BitmapData.loadBitmap("bg" + _root.bgNum );
_root.bg.attachBitmap(bgImage, 0, "auto", true);