Herencia y visibilidad

 <?php

        class A {

            public $aa = "aa";
            private $bb = "bb";
            protected $cc = "cc";

        }

        class B extends A {

            public $dd = "dd";
            private $ee = "ee";

            function test() {
                echo $this->aa;
                echo $this->bb; //Esta no la imprime
                echo $this->cc;
                echo $this->dd;
                echo $this->ee;
            }

        }

        $obj = new B();
        $obj->test();

        echo $obj->aa;
        echo $obj->bb;//Esta no la imprime
        echo $obj->cc;//Esta no la imprime
        echo $obj->dd;
        echo $obj->ee;//Esta no la imprime