Actionscript error cannot import library

In the Below action script file i get an error saying cannot import mx.controls.Label,how is this to be resolved

  package {
    import flash.display.Sprite;
    import mx.controls.Label;

    public class cl开发者_如何学Cd extends Sprite
    {
        public function cld()
        {
            var myLabel:Label = new Label();
            myLabel.text = "hello";
            addChild(myLabel);
        }

    }

}

Make sure it is Flex project and that in project properties->Flex Build Path->Library Path you import the framework.