Given these classes:

Given these classes:

class A {
    public function foo() {
        return "A";
    }
}
class B extends A {
    public function foo() {
        return "B" . parent::foo();
    }
}
class C extends B {
    public function foo() {
        return "C" . parent::foo();
    }
}
$obj = new C();
echo $obj->foo();

What is the output?