protected function choose_hits(array $response) {
        $allhits = $this->get_all_hits($response);
        $chosenhits = array();
        foreach ($allhits as $placeno => $hits) {
            foreach ($hits as $itemno => $hit) {
                $choice = $this->get_right_choice_for($placeno);
                $choiceitem = "$choice $itemno";
                if (!in_array($choiceitem, $chosenhits)) {
                    $chosenhits[$placeno] = $choiceitem;
                    break;
                }
            }
        }
        return $chosenhits;
    }