public function applyOrder($order)
    {
        if ($order == 'new') {//按发布时间倒序
            $this->newest();
        } elseif ($order == 'hottest') {//热门问题
            $this->hottest();
        } elseif ($order == 'reward') {//悬赏问题
            $this->reward();
        } elseif ($order == 'unanswered') {//未回答问题
            $this->unAnswered();
        }
    }