function arep_form_alter(&$form, &$form_state, $form_id) {
  if ($form_id == "user_register_form") {
    //field licence number is required only if profession is nurse
    $form['field_license_number']['#states'] = array(
      'required' => array(
        ':input[name="field_profession[' . LANGUAGE_NONE . ']"]' => array(
          array('value' => t('8')),
          array('value' => t('9')),
        ),
      ),
    );
  }
}