What is the value displayed when the following is executed?

Assume that the code was executed using the following URL:
testscript.php?c=25

<?php
function process($c, $d = 25)
{
global $e;
$retval = $c + $d - $_GET['c'] - $e;
return $retval;
}
$e = 10;
echo process(5);
?>

• 25
• -5
• 10
• 5
• I don’t know

Answer:
-5