Nested inheritance in PHP

Just reference them in any class using $this.

class MyClassD extends MyClassC {
    function __construct()
    {
        echo $this->variableA; 
        echo $this->variableB;
    }
}

$var = new MyClassD;

See it work!

Since variableA is public in the base class, you can just access it directly like so: $MyClassDObj->variableB.

Since variableA is protected, you need to write a getter if you wanted to access it from outside the class, otherwise from within class D, you can access it just like variableB. A getter would look like this:

public function getVariableA()
{
    return $this->variableA;
}

And then you call $MyClassDObj->getVariableA();

Just like you'd get it from MyClassA.