What is the output of the following code? class A { public $a = 1; public function
__construct($a) { $this->a = $a; } public function mul() { return function($x) { return
$this->a*$x; }; } } $a = new A(2); $a->mul = function($x) { return $x*$x; }; $m = $a->mul();
echo $m(3);
A.
9
B.
3
C.
6
D.
0