example_dependent_options.php

function example_dependent_options($key) {

  $plakalar = array(1, 2); // These are keys from parent dropdown.

  $iller = array(
    '1' => array(
      '1' => 'Aladağ'
    ),
    '2' => array(
      '5' => 'Aşkale')
  );

  if (isset($iller[$key])) {
    return $iller[$key];
  }
  return array();
}